مشروع التخرج هو تدريب على البحث العلمي او بحث علمي يقوم به الطالب في احد فصول التخرج حيث يقوم بتحديد فكرة بحث او مشروع وبكثير من الاحيان اقتباس الفكرة من احد دكاترة واساتذة القسم ثم يقوم بتطبيق معرفته الجيولوجية وربطها في معارف اخرى اذا لزم الامر بوسطة العمل الميداني والمخبري للوصول الى نتائج تتفق مع اهداف فكرته البحثية ثم تفسيرها ثم كتابة تقرير في الدراسة التي قام بها (وهذا الجزء هو المنشور في هذه الصفحة بهدف الاطلاع على تجارب الطلبة السابقين للتعلم منها بكيفية الكتابة العلمية بعد تعديل الدكاترة الاخير)
ملاحظات ونصائح من اخطاء متكررة
* معظم التقارير في هذه الصفحة تنسيقها تالف لكن تسلسلها جيد (حتى الان). * اذا كان لديك فكرة لبحث ما يفضل ان تبادر بها وان تعمل على تطبيقها عوضاً عن الاعتماد على الدكاترة بالفكرة. * يتوجب مراعاة اهتمامك في اختيار اي ميدان تريد العمل به، فمثلا اذا كنت تميل للجيوكيمياء عليك اختيار احد الدكاترة المختصين بالجيوكيمياء وموضوع مختص بالصخور والجيوكيمياء وغير ذلك سيصبح ارهاق شديد عليك وضغط نفسي لا يحتمل. * يمكن القيام ببحث التخرج بمفردك ويمكن القيام به بمجموعات كحد اقصى 4 طلاب، يجب ان تتفقوا مع بعضكم البعض قبل قبول العمل مع بعضكم البعض. * عندما تذهب الى دكتور ليعطيك فكرة لتعمل عليها ويشرح لك جزء منها استمع له جيدا، وعند خروجك من مكتبه ابحث عن الشيء الذي قاله لك وتأكد انه من ضمن اهتمامك ولا تقبل الفكرة الا اذا كنت تفهم شرح الدكتور لها وانها تناسب قدراتك وفهمك للتخصص لتجنب الضغط النفسي. * اثناء اجراء خطوات البحث بالعمل الميداني او المخبري سجل كل شيء مباشرة على هاتفك او على دفتر صغير، ادق الملاحظات ولا تترك كل شيء لوقت كتابة التقرير لانك لن تعلم حينها ما الذي فعلته وكيف ستبدأ بالكتابة. * اثناء الكتابة، اي معلومة تحصل عليها من اي مصدر اياك ان تنقل المعلومة وتترك مصدرها بل انقل المعلومة وانقل المصدر الذي تحصلت به على المعلومة وغير ذلك سيصبح توثيق ما كتبته عملية معقدة جدا وغالبا لن تستطيع القيام بها بمفردك بل تحتاج مساعدة دكتور او مكتبة او احد الـ “نيردات” الملمين جدا في المجال الذي تبحث به، لذا تجنب هذا الامر.
Paleontology: is the study of the history of the life on Earth as based on fossils (age, formation, & evolutionary)
Fossils: any preserved remains, impression, or trace of any living thing from a past – are the key of understanding of past life – give clues about organisms lived ago – help to show that evolution has occurred – provide evidence about how Earth’s surface was changed over time
Age of fossils: youngest from Holocene to the oldest from archaean (> 4.48Ga) – Age of earth 4.6Ga, & the oldest fossils 3.5Ga – most fossils are found in sedimentary rocks – the oldest known fossils are cyanobacteria that produced structure called Stromatolites
The ancient atmosphere consists of CO, CO₂, H₂O, N₂, H₂, NH₃, CH₄, H₂S, & little free O₂
Table 1:1 Types of True FossilsTable 1:2 Hard parts of fossils (common mineral components)Table 1:3 The process of fossilization (taphonomy)
Conditions favorable for preservation
1. Rapid & permanent burial 2. Continued sediment accumulation 3. Lack of oxygen (O limits decay & scavenging) 4. Lack of heat or compression (destroy fossils) 5. Hard body parts (skeletal bones, exoskeletons)
Table 1:4 Formation of fossils
Body fossils
actual body or body fossils that preserved may be altered (chemically or physically)
1:5 Types of body fossils (Unaltered & altered remains) Table 1:6 Types of unaltered remainsmammoth: Pliocene 5Ma- Holocene 4,500yrTable 1:7 Types of altered remainsTable 1:8 Types of replacement in altered remains
Molds & Casts
Mold & cast: 3D preservation where the original is not present
As remains buried, they surrounded with sediment
Mold impression of skeletal (or skin) remains in an adjoining rock
If buried object hollow, it infilled with sediment, the actual buried object decays or dissolved, leaving internal & external mould
Casts: are formed when an external mould is infilled by sediment or precipitated minerals – appears as replica of original buried object – cast is original skeletal material dissolves cavity (mold) fills with materials
Framework silicate = Tectosilicate Number of O shared per T = 4 Si:O ratio = 1:2 Structural configration = Framework tetrahedra
INTRODUCTION
More than two-thirds of the Earth’s crust is composed of frarnework silicate minerals, because include quartz & feldspar
The structure of all these minerals is based on aframework of TO₄ tetrahredra – T is Si, or A1 3and each of the 4 oxygen anions is shared with another tetrahedron
Open structure lead to 2 consequences : 1. Composition: easily accommodate large cations (alkaline) due to largest coordination site (O with 6-fold & shear corner) if substitute Si by Al in T site 2. physical properties: law specific gravity (due to Occurrence, occur at law P in crust)
The common framework silicates, & occurrence in rocks quartz, plagioclase, & alkali feldspars are most abundant
calcite & dolomite groups share same structure & collectively called rhombohedral carbonates, because they have rhombohedral symmetry
Successive layers offset so that position of C is equivalent to cubic close packing, & repeated in every third CO₃ layer, comers of triangular CO₃ altemate by mirror plane every layer (ABC) result is exact duplicate layer of CO₃ groups is repeated only every sixth layer.
Divalent cations (Ca, Mg, Mn, & Fe) occupy octahedral (6-fold) sites, Each O coordinates with one C within its layer, one divalent cation above it, & one below
surfaces of 3 cleavage “rhomb” parallel to 3 edges of triangular carbonate groups
This discussion leads to a problem with nomenclature in rhombohedral carbonates
Solid Solutions
In calcite group: controlled by ionic radii – between magnesite Mg, & siderite Fe, & between siderite & rhodochrosite is complete – limited between rhodochrosite & magnesite – Limited between Ca (1.14) & Mg, Fe, Mn ionic radii (Mg 0.86), (Fe 0.92), (Ca 1.14), (Mn 0.96)
In dolomite group: Dolomite CaMg(CO₃), & ankerite Ca(Mg,Fe)(CO₃), form solid solution series, & some Mn may substitute for Fe or Mg
Aragonite Group orthorhombic aragonite structure favored for cations whose radius in octahedral (> 1.1A) & calcite structure favored for smaller cations (Because Ca²⁺ anionic radius = 1.14 A in octahedral) so fit in either structureCalcite Group
Calcite (Mineral)
Composition: – nearly pure CaCO₃ – because Crystallization at elevated T allows for some Mg, Fe, Mn, or Zn – Mg is common substation – Some larger cations (Ba or Sr) may present
Form – prismitic, Rhombohedral, scalenohedron
Iceland spar: High-quality clear calcite
Hexagonal (Rhombohedral)Dolomite GroupAragonite GroupAlteration in Aragonite commonly inverts to its polymorph calcite, & pseudomorphs of calcite after aragonite are common, also may be replaced by dolomite
OH-BEARING CARBONATES
Restricted to oxidized portion of Cu-bearing hydrothermal sulfide mineral deposit
Occurrence 1. produced when primary Cu sulfide, such as chalcopyrite, oxidized & altered by acidic water percolating down from surface 2. carbonate component acquired from CO₂, dissolved in meteoric water or from carbonates in host rock for mineral deposit
Include compounds in which cations of one or more metals are combined with oxygen
All of these minerals, except ice, are isodesmic, so they don’t contain anionic groups
Chemical bonding is dominantly ionic – except Ice (molecular crystal)
Most of minerals have high symmetry, reflecting fact that structures based on systematic packing of oxygen in cubic or hexagonal close packing
Cations occupy tetrahedral & octahedral sites between regularly packed anions
Oxides Conveniently grouped on basis of cation to oxygen ratio
XO groupX₂O groupXO₂ groupX₂O₃ groupor Hematite group X₂O₃ GROUP or Hematite group Structure All share a confirm on structure based on hexagonal close-packed oxygen anions, with metal cations occupy octahedral sites
Corundum Color
Blue : contains Fe & Ti Red : contain Cr Yellow & green : contain Fe³⁺ & Fe²⁺
XY₂O₄ GROUP or Spinal group
Crystalizes in isometric crystal system
Normal Spinal structure: displayed by spinal & chromite series
X cation accupy tetrahedral (4-fold) sites, & Y accupy octahedral (6-fold)
Structure based on cube close backing with X & Y cation in tetrahedral site & octahedral site among O ionsGeneral formula XY₂O₄ → X²⁺Y₂³⁺O₄
Inverse Spinal displayed by magnetite In magnetite unit cell contain 8Fe²⁺ in octahedra, the 16Fe³⁺ disrupted to 8 in tetrahedral & 8 in octahedral sites XY₂O₄ → X³⁺(Y³⁺Y²⁺)O₄XY₂O₄group or Spinal group
Metals essential for industrial society extracted from sulfide include copper, zinc, lead, antimony, molybdenum, cobalt, nickel, silver
sulfur are law δ- than O, have about 10-20% ionic character (covalent or metallic)
There is no agreed on classification scheme
General Formula
MpXr
M: metal or semimetal Such as: Fe, Zn, Cu, pb, Sb, or As
X: atoms Such as: S, As, S + As, or Te
Sulfosalts
metal + semi-metal + sulfur
classified based on chemical notions that have long since been abandoned
SULFIDE PARAGENESIS
Hydrothermal Deposits: sulfide & related minerals characteristic of hydrothermal vein & replacement deposits, deposited from hot aqueous solutions in void spaces or by replacement of rock
Essential features of hydrothermal system: 1. Water 2. Heat 3. Source for metals precipitated by water 4. Migration pathways 5. Precipitation site
Water: may bemeteoric, magmatic, metamorphic, or connate
Heat: by igneous intrusion, & burial
Source for metals precipitated by water: sulfur derived from crystallizing magma or leached out of rock by water
Migration pathways: Fluids flow via rock along fault, fracture, & normal pore space
Precipitation site: Minerals precipitate by filling spaces along faults, fractures, & in other voids, or by replacing minerals in rock
Supergene Processes
primary or hypogene mineralization produced in hydrothermal system extensively altered if exposed to nearsurface environment
metals found in sulfides form oxides, hydroxides, carbonates, & sulfates
Because reactions produce oxygen-bearing minerals at expense of sulfides, near zone is referred to as oxidized zone & result are called supergene or secondary minerals
Because pyrite are common sulfide, oxidized zones of most sulfide deposits colored yellow & red: iron oxides & hydroxide derived from it
These minerals insoluble & accumulate near surface to form encrusting mass “gossans”
Pyrite in deeper portions of super genealteration zone serve as host to extensive precipitation of copper sulfides in supergene enrichment process
sulfide-enriched or reducedzone: zone of concentrated mineralization at water table surface
Supergene processes cause extensive alteration of country rock hosting sulfide deposits
Excess acid produced by oxidation of sulfides neutralized by reaction with silicate & form clay
A typical reaction involves hydrolysis of K-feldspar (KAlSi₃O₈) to form kaolinite: 2KAlSi₃O₈ + 2H⁺ + H₂O → Al₂Si₂O₅(OH)₄ + 4SiO₂ + 2K⁺
Common mineral in oxidized portion*Chalcocite & Covellite differ in charge of sulfurCrystal System
Pyrrhotite Vs Pyrite
In Pyrrhotite principal variation in iron content 2Fe³⁺ + Φ –> 3Fe²⁺ (> 20% Φ)
Distribution – Only carbon, in the form of graphite, constitutes significant rock-forming mineral – other found as trace element (such as gold, silver, copper, & diamond, are rare & valuable)
Native element divided into 3 group 1. METALS 2. SEMIMETALS 3. NONMETALS
Part.1 : Metals & Semimetals
METALS
Divided into 3 group based on chemistry & structure 1. Gold group 2. Platinum group 3. Iron group
All have Isometric unit cell
bond: is strong metallic bond – all are soft, & malleable – all are good conductors of heat & electricity – All are sectile, & opaque
Structure is cubic close packing of metal, which yields face-centered cubic unit cellGold Group Substantial solid solution is possible between gold-silver & gold-copperGold Group All have isometric unit cellPlatinum & Iron Groups
SEMIMETALS
Bond: more covalent, directional than metals
Unit cell : Hexagonal
Occurrence: in hydrothermal sulfide deposits as primary or secondary mineral
Semimetals
Part.2 : Nonmetals
Sulfur structure
consist of 8-fold ring covalently bonded S-atoms, bond laterally via van der Waals
3 polymorphic variety known: 2 monoclinic & one orthorhombic Orthorhombic are commonTerm carbonado applied to black or grayish bort of diamondCrystal System
– Strong Center of Low P – Sustained winds > 74 mph, To be considered a Category 1 Hurricane – On average there are 45 hurricanes/yr – Size ranges from 60 miles-900 miles, with a typical size of about 400 miles – Can last from days to weeks
What do they need to form? – Consistent heating of the surface – High Humidities – Cumulus & Cumulonimbus Clouds
Formation Regions Hurricanes are called by other names (depending on where they occur) 1. Hurricanesin the Atlantic & East Pacific 2. Cyclonesin Indian Ocean near Australia 3. Typhoons off coast of China & Indonesia
The majority of tropical storms & hurricanes start out as tropical disturbances
unorganized masses of thunderstorms with very little organized wind circulation
During the hurricane season in the Atlantic Ocean & Gulf of Mexico, tropical disturbances often grow from a pattern of stormy weather, called an African easterly wave
These waves typically emerge every 3-4 days off the W coast of Africa & then drift W within the trade winds into the Atlantic Ocean
If weather & ocean conditions continue to be favorable, the system may then strengthen
Tropical Depression
As a system continues to become organized & winds begin to circulate, it become tropical depression, weakest form of tropical cyclone
It is called a “depression” because it has low, or depressed, air p at its center
As the system develops, winds converge towards the center P near the center drops
During this transition, the disturbance begins to obtain its energy from the ocean not from horizontal T gradients in atm & env.wind
Tropical Storm
As bands of thunderstorms continue to develop, the depression may intensify into a tropical storm with max sustained wind speeds of 63‐117.5 km/hr
A tropical storm usually forms in this manner (from intensifying tropical depression)
Once a system is classified as a tropical storm, it is given a name
Approx. 100 tropical cyclones / yr
Many of tropical cyclones die out before they can grow stronger, with only approximately half of them (50) eventually strengthening into a mature hurricane (or typhoon)
Hurricanes
If a tropical cyclone obtains a maximum sustained wind speed > 119 km/hr, it classified as a hurricane (Typhoon or Cyclone)
At this point, the recognizable, cloud‐free eye of a hurricane typically forms
In the Atlantic, Central oe E-Pacific, hurricane intensity classified based on max surface wind speed using the 5 categories of the Saffir‐Simpson Hurricane Wind Scale
Ingredients for Hurricane Formation
Warm ocean T > 27°C, deep 200m – need lots of evaporation – winds churn up water → WARM water – Both only happen equatorward of 20°N-S
Coriolis – needed to initiate the spinning – Need to be between > 5°N-S
Low values of vertical wind sheer – Necessary for the storm to organize
Hurricane Structure
As air rushes inward in spiral pattern bands of clouds & thunderstorms are formed
Closer to the “eye” you get: – The most severe thunderstorms – The most intense rain & wind – The eye wall has the highest wind & rain
There can be more than three sets of bands
Hurricane Intensification
The storm can intensify if there is: Weak vertical sheer: allows condensation energy to be concentrated over a small area
Moist humid air in the upper troposphere: lots of condensation
Cold upper atm conditions: leads to a large PGF
Hurricane Damage
Wind Damages – Hurricanes move at 45 mi/hr – converging air moves at a faster velocity – The velocity of the winds you experience depends on your location within hurricane ν.motion + ν.rotation (100 + 45) m/h = 145 ν.motion – ν.rotation (100 – 45) m/h = 65
Storm Surges – abnormal rise of sea along shore – result of strong winds – Can be as high as 7 m, Typically 1-2 m – waves around 6-15 m can occur
Flooding – Caused by intense rains that accumulate – Rain accumulation can be up to 10 ft/day – Typical numbers are 1-3 ft/day
Hurricane Classification Saffir-Simpson Scale
Hurricane Decay
When conditions become unfavorable the hurricane starts to decay
Colder sea surface T: < 80F will cause the storm to weaken or even dissipate
Land friction caused by large land mass, & their terrain cuts off the hurricane’s circulation, & squeezes out storm’s moisture
Shearing winds aloft – Tropical storms & hurricanes are vertically stacked systems – Hostile upper level wind conditions produce shearing, which blow off the high cloud tops of these storms, & causes them to become disorganized
Sinking air: subsidence from high P such as subtropical ridge can inhibit development. – Sinking air from high P hinders thunderstorm development, which is a critical element in hurricane strengthening
In general
Hurricane Watch – if poses a direct threat to an area – Issued 24‐48 hr before storm arrives – Issued by the National Hurricane Center
Hurricane Warning – if it appears that storm will strike an area – The warning is accompanied by a percent chance of the hurricane center passing with in 65mi of a particular community – Typically within 36 hours
Hurricane Impact
Flooding Storm Surge Wind Damage Energy of winds = wind V squared: E = V²
A doubling of the wind speed results in 4 timesthe destructive energy
Naming Hurricanes
If reach tropical storm strength (40‐74 mph)
Used to be all women’s names Now they alternate male‐female
Names “Retired” if cause enough damage
CENTRAL PACIFIC Has their OWN List that used for Hawaii
HURRICANE GROUP ACTIVITIY GROUP 1 : Super Typhoon Haiyan GROUP 2: Hurricane Katrina GROUP 3: Superstorm Sandy GROUP 4: Hurricane Patricia GROUP 5: Hurricane Rita GROUP 6: Hurricane Andrew Group 7: Galveston Hurricane Group 8: Hurricane Floyd Group 9: Hurricane Camille Group 10: Hurricane Wilma
rapidly rotating narrow region of low P – form during intense thunderstorms. – Wind speeds from 70-300 mph – P can be as low as 900 mb
Tornado Development
Step 1: Rotating body of air at the ground – This occurs because of vertical wind shear A. Wind speeds increase with altitude B. Drag & Friction: decreasing wind speed at surface
Step 2: Horizontal rotating air is lifted off the ground by the Updraft of Thunderstorm – MESOCYCLONE: the horizontal rotating air mass if lifted vertically
Step 3: Mesocyclone is fully developed in the updraft of a thunderstorm – If a tornado develops it descends from the slowly rotating wall cloud, in lower of cloud
Mesocyclone
vertical cylinder of rotating air, 3-10 km
Develops in the updrafts of severe T-Storms
Usually precedes tornadoes by 30 min
Stretching of the mesocyclone column causes faster rotation
Just like a figure skater, Something that begins with a larger diameter rotating at a slow speed begins to rotate faster as the tube is elongated & the diameter
Thunderstorm & Tornado
From the wall cloud a very narrow, fast rotating structure emerges
This forms a funnel cloud (as long as the cloud does not touch the ground)
As soon as the funnel cloud touches the groundit is called a tornado
Suction Vorticies
Some tornadoes have multiple suction vortices
Intense areas of high winds that are part of ONE tornado
There can be 4-6 suction vortices
The stronger the tornado the more vortices Weak tornadoes usually don’t have them
Tornado Classification
Classified as WEAK: rope like & narrow STRONG: the classic funnel shape VIOLENT: have lots of debris associated with them & can be quite dark in color
Fujita & Enhanced Fujita Scale – Scale for Damage caused by tornadoes – Wind Speed, Amount & Type of damage
There are 2 scales used Fujita Scale (F) Enhanced Fujita Scale (EF)
They can form in 1. conjunction with mid-latitude cycloneon the edge of a Cold-Front 2. conjunction with hurricanes
Occur in the foothills of the Rocky Mountains
Associated with drylines, different humidity
Thunderstorm Formation
Form when warm, & humid air rises in a conditionally unstable or unstable env.
There are 2 categories: 1. Air Mass Thunderstorms: formed by unequal heating of the Earth’s surface within a maritime tropical (mT) air mass 2. Severe Thunderstorms formed by unequal heating & lifting of warm air along a frontor mountain
Air Mass Thunderstorms
Happens inside an air mass (mT)
Usually in spring & summer, mid-afternoon
Not associated with a front
Due to local differences in T
Thunderstorm Life Cycle
Like mid-latitude cyclones, T-Storms have a Life Cycle
Stages of Development Stage 1: Cumulus Stage Stage 2: Mature Stage Stage 3: Dissipating Stage
The Cumulus Stage – Rising air only, Makes a bigger cloud – Moisture is being added to higher altitudes – Needs a continuous supply of moisture
The Mature Stage – Precipitation, by the Bergeron Process – Rain begins to fall, downdraft – Updrafts & downdrafts exist side by side – Most active stage: winds, lightning, rain, hail
Dissipating Stage – Cooling effect of falling precipitation – influx of colder air up topmark it’s END – Downdraft cuts off updraft – Cloud stops growing – You’re left with weakly descending parcels – The cloud basically KILLS itself
downdraft (air going down)
form for two reasons
Entrainment: mixing of dry air with cloud air at the edge of the cloud – Causes the cloud drops to evaporate – Energy comes from the T of the air parcel – Temperature drops, parcel cools – Cooler air sinks to the surface
Drag: Air dragged downwards as precipitation falls
Severe Thunderstorms
Heavy downpours, flooding, gusty straight-line winds, large hail, lightning & tornadoes! – NOT Common on Hawaii & Pacific Islands
To be classified as Severe: Must have winds in excess of 93 km/h hail 0.75 inches a confirmed tornado
Persist for many hours Vertical wind sheer causes precipitation to fall in downdraft, allowing the updraft to retain strength – Sometimes the updraft is so strong you get overshooting tops & anvils
Cold air of the downdraftsmaking: mini cold front (GUST FRONT or Outflow Boundary) Can form a Roll Cloud
Supercell Thunderstorm
Causes dangerous weather Large, very powerful, up to 20 km in height Last many hours 20-50 km in diameter
Vertical wind profile may cause the updraft to ROTATE!
MESOCYCLONE usually spawns Tornadoes
Need a lot of Latent Heat – Requires moist troposphere – An inversion a couple of km above the surface (caps moisture) – Unstable air can break through the inversion by “eroding” it
Lightning and Thunder
Lightning is uliain Hawaiian Thunder is hekiliin Hawaiian
A storm is classified as a thunderstorm only after thunderis heard,
Because thunder is produced by lightning
Lightning is a discharge of electrical energy
Essentially a giant “spark” between regions of positive (+) & negative (-) charge
Lightning
Occur Between 1. cells in same storm: inter-cloud lightning 2. Within a cloud: intra-cloud lightning 3. Cloud to air 4. Cloud to ground (CG)
Forms if a charge separation occurs in cloud 1. Earth trying to equalize electrical difference 2. – ve charges want to flow to the ground
Lightning Formation (Charge Separation)
We don’t exactly know why it happens
One theory: – Hail stonestend to have a warmer surface than ice crystals – When warm hail collides with colder ice, electrons transfer from ice to hail – Hail (-) is bigger & heavier & settles toward the bottom of the cloud – Smaller (+) ice crystals are lofted to the top
Excess electrons cause the air to ionize: Rip molecules apart (N₂ or O₂ become N+, O-) – Air is normally very INSULATING – Ionized air is very conducting – like a metal – Ionized air forms tubes of 50 m in length & 10 cm in diameter (LEADER) – A bunch of leaders that are connected is called a STEP-LEADER. – NOTE: There still hasn’t been a flash yet!!!
Each electron contains LOTS of energy When it reaches the surface the energy is RELEASED as HEAT, Electrons are drained at the surface first so the FLASH starts at the ground, Can have several (3-4) in rapid succession (1/10 of a second apart) (lead by a DART LEADER)
– This is why lightning is said to GO UP, rather than down
The movement is STILL from CLOUD to GROUND–But the “heating” happens at the surface FIRST.
The electrons closest to Earth are “discharged” first
Heatthat is released causes air around a step-leader to reach 30,000°C (54,000°F) The warmer, the shorter the shorter the wavelength
Thunder
When air is heated quickly a shockwave forms & causes thunder
Similar to planes crossing the sound barrier, firecrackers & gun shots
Sound travels at 330 m/s or 1000ft/s
If thunder takes 3 seconds to happen after observing lightning then the storm is:–3 s * 1000 ft/s = 3000 ftaway (6/10 of a mile away).
Is big blob of air with similar properties – Usually 1600 km across & Several km thick
FRONTAL PASSAGE Change in weather when one air mass moves out & a new air mass moves in – Brings changes in T, P, RH, & Winds
Air masses form when they move over large regions that exhibit very similar properties
Air mass Source Regions
Polar & Tropical regions tend to exhibit such properties & therefore are good source regions
The mid-latitudes tend to be strongly variable & therefore are not good source regions
Types of Air masses
Air masses are designated by 2-letter describes basic info about T & RH – T: Cold (Polar) or warm (Tropical) – RH: wet (Maritime) or dry (Continental)
Symbols used Polar (or Cold) → P Tropical (or warm) → T, (Thenderstorm) Continental (or dry) → C Maritime (or humid) → M Equatorial (from the Equator) → E Artic (from Artic) → A Antartic (from Antartic) → AA
For Example mP = Maritime Polar = Cold & wet
Polar Front Theory (or Norwegian Cyclone Model)
Discovered by Norwegian scientists during World War I
Theory Mid‐Latitude Cyclones (MLCs) – Develop in conjunction with the Polar Front – Cold equatorward moving air collides with warm poleward moving air – The collisions create FRONTS – In upper atm polar front is continuous – at the surface polar front is discontinuous
Pacific Mid-Latitude Cyclones
Fronts
Boundaries surfaces that separate air masses of different densities (related to T) – the barrier that travels with air masses
Can be combinations of warm, cold, dry, moist
Usually 15‐200 km wide bands but narrow
Represented by narrow lines on a map
Overrunning: Warmer air (less dense) always moves above cooler air
Ideally the fronts move in approx. the same direction
Weather Behind a Cold Front
Weather behind cold fronts is characterized by SUBSIDING air
usually a continental polar (cP) air mass
usually cloudless
generally stable, limits cloud development
Warm Front,Gradual SlopeWarm Front,A warm front cloudsCold Front, Slope is steepCold Front,A cold front cloudsStationary Front, Air flow parallel to frontOccluded Front
Single‐Cell Model First idea Solar energy drives the winds Problems : Doesn’t account for rotation & in this model the whole earth is an ocean without a continentals3‐Cell Model Hadley Cell Equator & 30 N-S Ferrell Cell 30 N-S & 60 N-S Polar Cell 60 N-S & 90 N-S
Three Cell Model
Horse Latitudes
The Horse Latitudes are 25‐30 N-S
Trade winds weaken in this region, & would stall early Spanish ships sailing to NewWorld
When particular areas were too calm, they were forced to toss over their frightened horses into the sea, or eat them
The legend is the horses would swim after them for miles before they drowned, & the superstitious sailors would hear the horse screams in their haunted dreams for the rest of the voyage
Westerlies
Occur between 30‐60 N (S) Latitude
Blowing from the high P area in horse latitudes towards the poles
Steer extratropical cyclones
Can redirect Tropical Storms
The Westerlies are: 1. strongest in winter hemisphere & times, when the P is lower over the poles 2. weakest in the summer hemisphere, when P are higher over the poles
The strongest westerly winds in the middle latitudes can come in the Roaring Forties, between 40° & 50° latitude S
Roaring Forties (& Furious Fifties)
The strong west‐to‐east air currents are caused by the combination of air being displaced from the Equator to S Pole & the Earth’s rotation, & there are few landmasses toserve as windbreaks
Jet Streams
Region of the upper atmosphere where a narrow band of airmoving REALLY fast
Location of jet stream influences local weather
LARGE T contrasts
Polar Jet Stream (Mid‐Latitude)
Where the Polar Frontis located: Where the cold polar easterlies interact with the warm westerlies
It’s Geostrophic Wind if it’s high up in atm
Meanders west to east
Can exceed 500 km/hour In winter it travels at 75 km/h In summer 65 km/h
Subtropical Jet Stream
Semi‐permanent jet that exists over the subtropics
Is mainly a wintertime phenomenon
Due to the weak summertime T gradient, the subtropical jet is relatively weak during the summer
Slower than the polar jet
Still travels west to east
Usually at about 25 N
Usually at an altitude of about 13 km
Global Winds & Ocean Currents
Winds are the driving force for ocean currents
A relationship exists between ocean & atmosphere circulation
Ocean currents move more slowly than prevailing winds
Pacific Trash Vortex
Trash gets “Stuck” in the N Pacific Gyre
Floating mass of trash
Mostly Plastic that is non‐biodegradable
Rubber duckies got free & went all over the world following ocean currents
El Niño & La Niña
El Niño Southern Oscillation
Ocean phenomenon that occurs in the Equatorial Pacific
As the southeast trade winds decrease in strength (weaken) the warm water can make it farther across the Pacific to wards S American
Named because it starts during Christmas
Usually happens every 3‐7 years
P changes & reversals in the Pacific trigger the change in winds
La Niña Events The opposite of an El Niño When T colder than average T in the Pacific
Volcano is a mountain formed of lava & pyroclastic materials
Crater depression at a summit of a volcano
Caldera is a Crater with depression> 1 km – Nearly circular – formed by collapse
Conduct (pipe) carries magma to the surface where it’s extruded from a surface opening called a vent – connects magma chamber to the surface – rare type to depth 200km in S Africa – necks Volcanoes on land weathered, eroded, but in pipe is more resistant & remain standing for a long while & is named neck
Vent opening in the surface via which molten rocks & gases are released
Fumaroles Vents that emit only gases
Parasitic Cones produced by volcanic activity from fissures along the flanks
Volcanoes
ViolentVolcanoes: ring of fire, produce Pyroclectic materials
Quite Volcanoes: produce lava, like Hawaii
Lava flow – It comes out from the quiet volcanoes – 90% by volume are basaltie in composition
Pahaoehoe (ropy) Lava – It’s name comes from Hawaii – 10 to 300 m/hr – Resembles braids in ropes – control: fire boats
Aa lava – It’s name comes from Hawaii – 5m/hr – Rough , jagged blocks
Viscosity
Is The measure of a material’s resistance to flow
Eruptions & Viscosity determine by 1. Composition of the magma Granitic, Andisitic, or Basaltic 2. Temperature of the magma 3. Dissolved gasses in the magma – gas 1 – 5 % by weight – H₂O 70%, CO₂ 15%, N₂ & SO₂ 10%, Cl₂,H₂, Ar – provide the force to extrude lava – gas are expand near the surface
Pyroclastie materials comes out from the violent volcanoes. Those are ejected pulverized rocks , lava & glass fragments Blocks if made of hardened lava Bombs if lava twisted after ejected in the air
Volcanic structures & eruptive styles
Shield volcanoes broad, gently sloping, built from fluid basaltic lava – Hawaiian islands (MaunaLoa) > 9km high – Flanks have gentle slopes of a few degrees
Cinder cones small, built of pyroclastic materials ejected from a single vent – They have a steep slope angle – Frequently occur in groups
Composite cones(strato voleanoes) composed of inter bedded lava flows & pyroclastic materials – located around pacific ocean (ring of fire) – Large conical shape with steep summit – more gradually sloping flanks – Magna gas-rich with andesitic composition – Most violent type of activity (explosive) – Ex: Saint Helens, Andes mountains – most destructive because of: 1. Pyroclastic flow (hot gas + Ash) which move down slope with speed 200Km/hr 2. Lahars (mud flow)
Fissures eruptions Volcanic materials are extruded from fractures in the crust – Long narrow cracks emit low-viscosity fluid of basaltic lava termed fluid basalts – Landscape buried by these lava produce basalt plateaus
Intrusive igneous activity
Plutons(Intrusions) are structures that result from the emplacement of magma into preexisting rocks beneath the earth surface
Intrusive igneous bodies (Plutons) are classified according to shape & orientation with respect to the host rock
Tabular intrusive bodies
Sills are horizontalconcordantbodies where magma is insetal between sedimentary beds – can change into discordant (Dike) by change there orientation
Dikes are discordant bodies that cut acoss bedding surfaces in the host rock – can change into concordant (Sill) by change there orientation
Massive intrusive bodies
Batholiths largest intrusive bodies, usually felsic or intermediate rock, discordant – can change into concordant (laccolith) by change there orientation
Laccolith igneous body, injected betweem sedimeniary strata & arcs the beds above – can change into discordant (Batholiths) by change there orientation
Sill tabular, concordant, low Viscosity, Basaltic Dike tabular, discordant , low Viscosity, Basaltic Laccolith massive, concordant, high Viscosity, Granitic Batholith massive, discordant, high Viscosity, Granitic
Plate tectonics & igneous activity
Most active volcanoes are – composite cones, emit volatile-rich magma – having intermediate composition – located along the margins of ocean, within circum, pacific belt
Deep ocean basins, include oceanic ridges & basaltic shield volcanoes (Hawaii)
we can find all volcanoes types in Interior of the continents
Zones of igueous activity
Voleanism at convergent boundaries – Subduction of oceanic slab triggers partial melting in upper mantle at depth of 100 km – Partial melting caused by addition of volatiles (water) derived from the sunducting plate – Volcanie island ares such as Marianns & coutinental volcanic ares are formed (Andes)
Volcanism at divergent boundaries – Greatest volume of magma (60%) is produced along oceanic ridge system – Tensional forces in the lithosphere causes reduction of confining pressure in the mobile mantle triggering decompression melting – Partial melting produces basaltic magma
Intraplate volcanism(within the plate) – Hotter than normal mantle material ascends upwards (mantle plume) – It originates a the core-mantle boundary – When the plume head reaches the top of the mantle, decompression melting produces basaltic magmia that initiates volcanism hot spot
Vibration of Earth produced by the rapid release of energy
The movement of the ground, is caused by waves of energy released as rocks move along faults which means that earthquakes are associated with movements along faults
Fault a large fracture in rocks, from several m to Kms long, where rocks move along which displacement has occurred
Explained by the plate tectonics theory
Focus the point in Earth’s interior where the rocks start to fracture, origin of earthquake Epicenter the point on Earth’s surface directly above the focus
Elastic rebound theory
earthquakes occur as rock elastically returns to its original shape
Mechanism for earthquakes was first explained by H. Reid
Elastic Rebound Theory Rocks spring back into its original shape as stress removed
Elastic ReboundElastic Rebound
foreshocks & aftershocks
Earthquakes are often preceded by foreshocks & followed by aftershocks
Foreshocks indication, weak earthquakes, releas some of energy
Aftershocks followed the earthquakes, releas some of energy as crust return to its original shape (crust unstable)
Earthquake waves
Seismology Study of earthquake waves Seismograph Earthquake recording instrument, Records movement of Earth Seismogram Record made by seismograph
Types of earthquake waves 1. Body waves: Primary (P) & Secondary (S) 2. Surface waves
Seismographs have a weight freely suspended from a support that is securely attached to bedrockSeismogram records wave amplitude vs. time
Types of earthquake waves
Body waves: Primary waves (P) – Push-pull (compressional) motion – compression & expansion – First to be recorded at a seismograph – Travel through solids, liquids, & gases – Greatest velocity of all earthquake waves – longitudinal wave: Causes rock to vibrate in the same direction the wave is traveling
Body waves: Secondary waves (S) – Shake or transverse (shearing) waves – causes the rock to vibrate at right angles to the direction of travel (to the direction of propagation) – Travel only through solids – Slower velocity than P waves
Surface waves – Complex motion – Slowest velocity of all waves – The largest & most destructive – like ocean waves
Earthquake zones are closely correlated with plate boundaries 1. Circum-Pacific belt 2. Oceanic ridge system
When analysing an earthquake the first task seismologists undertake is determining its epicenter
To determine distance to epicenter 1. The difference in arrival times of P & S wave are determined from the seismogram 2. Using travel time graphs find the (S-P) interval on the vertical axis to determine the distance on the horizontal axisA time-travel graph is used to find the distance to the epicenter3 station are needed to locate epicenter Circle equal to the epicenter distance is drawn around each station epicenter is at Point where 3 circles intersect
Principle for study Earth’s interior
Most of our knowledge of Earth’s interior comes from the study of P & S waves
Travel times of P & S waves via Earth depend on properties of materials
Velocity of waves increases with depth.
Seismic waves are refracted as they pass through the earth
Waves follow strongly curved paths
S waves travel only through solids
Seismic waves follow curved paths
Earthquake intensity and magnitude
Intensity A measure of the degree of earthquake shaking at a given locale based on the amount of damage – measured by the Mercalli Scale
Magnitude amount of energy released – Concept introduced by C.Richter – Measured using the Richter scale or Moment Magnitude scale
Magnitude Scales
Richter scale – Based on amplitude of largest wave – logarithmic scale: 1°→1, 2°→10, 3°→100 – Each unit = to 32-fold energy increase – Doesn’t useful for large earthquake (>7)
Moment magnitude scale – Measures very large earthquakes – Derived from the amount of displacement that occurs along a fault zone
Factors that determine structural damage 1. Intensity of the earthquake 2. Duration of the vibrations 3. The design of the structure 4. Nature of the material upon which the structure rests
Destruction results from 1. Ground shaking 2. Liquefaction of the ground 3. Tsunami, or seismic sea waves 4. Landslides & ground subsidence 5. Fires
Liquefaction caused by 1. Saturated material turns fluid 2. Underground objects float to surface – during Liquefaction water-saturated soil behaves as a fluid. It becomes incapable of supporting much weight – such as sandy soil
Tsunami travel times to Honolulu
Earthquake prediction
Short-range prediction – no reliable method yet devised
Long-range forecasts – Premise is that earthquakes repetitive – Region is given a probability of a quake
Earth’s Layers defined by composition
Crust Thin, rocky, & outer layer
Continental crust – Upper crust composed of granitic rocks – Lower crust is more akin to basalt – Average density is about 2.7 g/cm³ – older than oceanic (Up to 4Ga) – thickness 35-40 km – thickness at some mountainous 70 km
Oceanic Crust – Basaltic composition – Density about 3.0 g/cm3 – Younger (<180Ma) than the continental – thickness 7km
Mantle : Below crust to 2900Km depth – Composition : of the uppermost is igneous peridotite & changes at greater depths
Core : A sphere having a radius of 3486 km Location Below mantle – Composition : iron-nickel alloy – density ≈ 11 g/cm3
SynclinesFold downfolds in strata – found in association with anticlines
Domes circular or elongated structure, produces by upwarping of the crust – Older rocks are exposed in the center – the youngest rocks exposed in the flanks
Basin circular or elongated structure, produces by upwarping of the crust – youngest rocks are exposed near the center – the oldest rocks exposed near the flanks
Faults: are fractures in the crust along which displacement has taken place
Every fold has 2 limbs Symmetrical Fold : if dip angle of 2 limbs equal each other Asymmetrical Fold : if dip angle aren’t equal Overturned Fold : the 2 limbs dipping in tha same directionDomesFault
Faults
Dip- slip Faults: movement parallel to dip 1. Normal fault: occur if the hanging wall block moves down relative to the footwall 2. Reverse fault: hanging wall block moves up relative to the footwall block 3. Thrust fault: reverse with dips < 40°
Strike-slip faults are faults in which the movement is horizontal & parallel to the trend, or strike, of the fault surface
fault-block mountains
formed as large blocks of crust are uplifted & tilted along normal faults
Grabens formed by downward displacement of fault-bounded blocks
Horsts are elongated, uplifted blocks of crust bounded by faults
Mountain Building
Folded Mountains formed by compressional forces
Orogenesis result in forming of mountains
Young mountain belts (less than 100Ma): 1. American Cordillera 2. Alpine-Himalaya chain 3. volcanic island arcs (Philippines, Japan)
Older mountain belts 1. Appalachians in N-America 2. Ural Between Europe & Asia
Occurrence
Most mountain building occurs at convergent plate boundaries
Colliding plates provide the compressional forces that fold, fault, & metamorphose the thick layers of sediments deposited at the edges of landmasses
Accretion process that occurs when crustal fragments collide with & stay connected to a continental plate
Accretionary wedge is the accumulation of different sedimentary & metamorphic rocks with some scraps of ocean crust
Terranes any fragments that have a geologic history distinct from that of the adjoining fragments – Terranes occur along the Pacific Coast
Ocean-Ocean ConvergenceOcean-Continental Convergence At a convergent boundary a collision between the continental fragments will result & form folded mountainsMountain Building by Continental Accretion
What is the order of events from oldest to youngestWhat is the order of events from oldest to youngestWhat is the order of events from oldest to youngestWhat is the order of events from oldest to youngestWhat is the order of events from oldest to youngest
Relative events are arranged in their order of occurrence (without date)
Ex. in a sequence of flat lying rocks, shale is on top of sandstone. The shale is younger, but how much younger is not known
Absolute the actual age of the geologic event
This is usually done using a radiometric- dating technique
Principle for Relative Geologic Age
Original Horizontality sedimentary rocks are deposited as horizontal layers – Any marked deviation from horizontality indicates deformation of the crust occurred after deposition of the inclined layer
Law of Superposition: in an ordinary vertical sequence of sedimentary rocks, the layer at the bottom of the sequence is oldest, & successively higher layers are successively younger
Cross-Cutting Relationship Principle Younger features cut older
The Principle of Inclusion if rocks or rock fragments are included within another rock, the rock fragments must be older
According to superposition Law A must have been deposited first (oldest) D must have been deposited last (youngest)The cross-cutting relationships Principle A is the oldest since it is intruded by dikes B older than dike C since it is cut by dike C Therefore A followed by dike B & then dike CThe sedimentary sequence A – D (oldest to youngest) have been deposited first A – D was then folded & subsequently eroded (erosion surface E) After erosion, F was depositedA & B are offset by fault D, so they have been formed prior to faulting, & C isn’t offset so it have been formed after faulting occurred(A) Sedimentary beds 1–3 were deposited as horizontal layers. Sometime later, a normal fault occurred (B) Sedimentary beds 1–7 were deposited as horizontal layers. Later, these beds were folded into an anticline. Later still, the anticline was truncated by an erosional unconformity, & finally, an 8 was deposited as a horizontal layer Inclusions of older rock fragments (from 1–7) found at the base of 8
Unconformities
Unconformity is a surface that corresponds with a gap in sedimentation, due to erosion & nondeposition
Rocks above an unconformity are younger than those below it
3 types of unconformities angular unconformity in which beds above & below the surface aren’t parallel nonconformity sedimentary layers overly crystalline rocks (igneous or metamorphic) disconformity in which beds above & below the surface are parallel, but the surface itself is irregular, exhibiting evidence of erosional relief
In geologic block diagrams & cross-sections, unconformities are drawn as wavy line
Geologic Time Scale
By correlating outcrops from place to place, & using the Principle of Superposition, it has been possible to determine the sequence in which sedimentary rocks were deposited.
This information, coupled with the fossil record, led to the development of the Geologic Time Scale.
The various subdivisions are based on major changes in the history of the Earth as documented by the geologic record.
The time scale is a relative time scale, & Ages are attached to the various geologic periods using radiometric dating.
that the geologic time scale is based on the sedimentary record while radioactive dating is applied to igneous & metamorphic rocks
Radiometric Dating
Radioactive decay spontaneous breakdown of a nucleus
The radioactive isotope is the Parent Isotope & the decay product is the Daughter Isotope
half-life of a radioactive element is the length of time it takes for 50% of the parent isotope to decay
The mineral zircon, which contains trace amounts of U but usually no Pb, is often used to determine the age of igneous rocks. The idea is that the zircon grains crystallized from the magma & therefore are the same age as the rock
exponential relationship
Exercises
Arrange the events from oldest to youngest1. Arrange the events from oldest to youngest 2. between C & E (& B) there is unconformity, What is the name of unconformity? 1. Arrange the events from oldest to youngest 2. between H & A (& F) there is unconformity, What is the name of unconformity? A is a sandstone (sedimentary rock) B is a basalt dike (tabular igneous intrusion) C is a diorite dike (tabular igneous intrusion) Zircon grains are separated from the basalt dike & the diorite dike & The number of 235U & 207Pb atoms is determined for a zircon from the basalt dike & diorite dike. The data are shown in the table. Because we want to calculate the age in millions of years, λ = 9.8458 x 10-⁴ my-¹
For each of the following diagrams, label with letters & numbers each layer, body, fault, & unconformity, & then determine the correct order in which the various rock units & other features occurred
Complete Table 2 by filling in the Age columnUse your knowledge of relative dating to determine the correct sequence of rocks in the diagram. Using the absolute ages you calculated in exercise above
المضرب: خط وهمي أفقي موجود على سطح الطبقة ويمر بنقاط ذات ارتفاع واحد على سطح الطبقة، وهي خطوط متوازية، ولها اتجاه واحد، والمسافة العمودية بينها متساوية.
خطوط المضرب توضح ارتفاعات سطح الطبقة، وخطوط الكنتور توضح ارتفاعات سطح الأرض
مقدار المضرب: وهو قيمة ارتفاعه من سطح البحر اتجاه المضرب: يحدد بالبوصلة الجيولوجية وهو عمودي على اتجاه الميل الحقيقي للطبقة
فترة الكفاف: المسافة الرأسية بين أي خطي مضرب متتاليين المسافة المضربية: المسافة الافقية بين خطوط المضرب
خطوط المضرب تتقارب من بعضها البعض إذا كان ميل الطبقة شديدا وتتباعد كلما قل، أي أن المسافة المضربية تتناسب تناسبا عكسيا مع الميل، وتتناقض قيم منسوب خطوط المضارب في اتجاه الميل أي المضرب الذي يلي مضرب ۷۰۰ في اتجاه الميل هو مضرب ۹۰۰ ويليه مضرب ٥٠٠ وهكذا True dip الميل الحقيقي Contour interval فترة الكفاف Strike interval المسافة المضربية ل
الميل الحقيقي والظاهري
الميل الحقيقي: زاوية الميل الأعظم بين مستوی سطح الطبقة والمستوى الأفقي وهو عمودي على خطوط المضرب في اتجاه تناقص قيم الخطوط
زاوية ميل الطبقة: الزاوية المحصورة بين خط الأفق وسطح الطبقة، ويحدد مقدار واتجاه زاوية الميل بالبوصلة الجيولوجية ظل (زاوية الميل) = فترة الكنتور \ المسافة المضربية tan(θ) = CI/SI
الميل الظاهري : الزاوية بين مستوى الطبقة ومستوى أفقي في أي اتجاه غير اتجاه الميل الأعظم، قيم الميل تتناقص في اتجاه خط المضرب حتى يصل صفر وتتزايد مرة أخرى ظا (الميل الظاهر) = الكنتور/المسافة المضربية الظاهرة tan(θ) = CI/SI
المسافة المضربية الظاهرية يتزايد الميل الظاهري باتجاه خط المضرب (زاوية الميل الأعظم) باتجاه الميل الحقيقي، ثم يقل حتى يصل للصفر باتجاه المضرب ويتزايد مرة أخرى وهكذا..
True Dip Angel الميل الحقيقي
خطوط المضرب والميل الحقيقي والميل الظاهريالميل هو انحراف الطبقة عن الأفق ولا علاقة له بالانحدار
الانحدار: انحراف سطح الأرض عن الوضع الأفقي بالطبقات وقد يتفق الميل والانحدار باتجاه واحد، وقد يكون اتجاه أحدهما عكس اتجاه الآخر
حساب زاوية الميل
في الشكل بالاسفل (المثلث ا، ب، ج) ا-ب = المسافة المضربية ب-ج = الفترة الكنتورية tan (θ) = CI/SI
عادة ما تكون الفترة الكنتورية = ۱۰۰م، وهي تمثل الفرق بين قيمة خطي مضرب متتاليين
ا
Ex. Calculate the Strike Interval (SI), If you know that the strata is Inclined at an angle of 30°, & the map scale 1:10,000
CI = 100m θ = 30° tan(θ) = CI/SI → SI = CI/tan(θ) SI = 100m/tan(30°) = 173m——i 1 cm on map = 10,000cm actual 1 cm on map = 100m actual 173m = 1.73cm on map———ii
نقطة الظهور ومكشف الطبقة
نقطة الظهور: نقطة يظهر فيها سطح الطبقة عند سطح الأرض أي أن نقطة الظهور هي نقطة مشتركة يكون فيها منسوب سطح الطبقة مساويا لمنسوب سطح الأرض (يتساوی عندها منسوب خط الكنتور مع منسوب خط المضرب)
تستخدم نقاط الظهور لرسم خطوط المضرب ومكشف الطبقة
مكشف الطبقة: الجزء الظاهر من الطبقة على سطح الأرض
لرسم مكشف الطبقة
رسم مكشف الطبقة بمعلومية ٣ نقاط ظهور مختلفة بالقيم ١. نمد خط بين اقل نقطة واعلى نقطة ٢. نجزء الخط الى عدة اجزاء تساوي الفرق بين منسوبيهما مقسوما على الفترة الكنتورية ΔSL/CI ٣. نمد خط من النقطة الثالثة من اطار الخريطة الى الاطار يمر في منتصف الخط بين النقطتين (الاعلى والاقل) ٤. نمد خطين من الاطار الى الاطار كل واحد يصل بنقطة من النقطتين الاعلى والاقل موازيان للخط الاول ٥. نمد خطوط اخرى تساوي عدد الخطوط المحسوبة بالخطوة ٢ ٦. نقيس المسافة بين الخطوط باستخدام المسطرة فنحصل على المسافة المضربية ونكمل رسم خطوط المضرب للخريطة ٧. نحدد جميع نقاط الظهور (النقاط الاي يتساوى فيها الكنتور مع المضرب) ونمد بينها خط يصل بها جميعها وهو مكشف الطبقة
رسم مكشف الطبقة بمعلومية ٣ نقاط اثنتين منهما متساويات ١. نمد خط من الاطار الى الاطار يمر بالنقطتين المتساويات ٢. نمد خط موازي له على طول الخريطة ٣. نقيس المسافة بين الخطين ونتبع الخطوات بالحالة الاولى (٦ و٧)
لرسم خطوط المضرب بمعلومية مكشف الطبقة ١. نحدد جميع النقاط التي تتقاطع بها سطح الطبقة مع خطوط الكنتور ٢. نرسم بينها خطوط تمر بنقاط متساوية بالارتفاع ٣. نقيس المسافة بينها فنحصل على الفترة المضربية ونكمل الخطوط
سمك الطبقة
سمك حقيقي: مسافة عمودية بين سطحي طبقة علوي وسفلي سمك رأسي: مسافة راسية بين سطحي طبقة علوي وسفلي سمك ظاهري: مسافة بين منحنى ظهور السطح العلوي ومنحنى ظهور السطح السفلي للطبقة عند موضع معين، ويتوقف على زاوية ميل الطبقة وانحدار سطح الأرض
أب = السمك الحقيقي اج = السمك الراسي الظاهري للطبقة جتام = السمك الحقيقي / السمك الرأس
حساب عمق الطبقات المائلة من الآبار
يعرف عمق الطبقة عند نقطة معينة بأنه المسافة الرأسية من سطح الأرض إلى سطح الطبقة العلوي أو السفلي، ويؤخذ العمق عادة بالنسبة للسطح العلوي ما لم يذكر غير ذالك
لتحديد عمق طبقة مائلة تحت السطح من بئر حفر على سطح الأرض ١. نجد ارتفاع البئر (من قيمة خط الكنتور الذي يمر بحفرة البئر) ٢. نطرح من ارتفاع البئر ارتفاع سطح الطبقة (من قيمة خط المضرب للسطح “ارتفاع سطح الطبقة”) عمق الطبقة = منسوب سطح الارض – منسوب سطح الطبقة عمق الطبقة = الكنتور لنقطة البئر – المضرب علىللطبقة
احسب عمق الطبقة (E) عند النقطة (أ) النقطة أ تقع على خط كونتور ٧٠٠م ويمر منها خط مضرب بمنسوب ٥٠٠ ،اذا عمق الطبقة عند أ = ٧٠٠ – ٥٠٠ = ٢٠٠م
رسم القطاع الجيولوجي للطبقات المائلة
١. رسم القطاع الطبوغرافي ٢. نحدد على شريط الورق تقاطع مكشف أسطح الطبقات مع خط القطاع، ثم ننقل هذه النقاط على المحور الأفقي للقطاع ٣. ترفع هذه النقاط رأسيا حتى تقابل خط البروفايل ٤. نرسم خط افقي أعلى البروفيل، ومن أحد نهايتيه نرسم زاوية الميل بواسطة منقلة باتجاه الميل ٥. نرسم خطوطة موازية لخط زاوية الميل وتمر بنقاط أسطح الطبقات الموجودة على خط البروفايل يمكن أيضا رسم هذه الطبقات باستخدام خطوط المضرب أي تقاطع خطوط المضرب مع خط القطاع، وباستخدام ثلاث نقاط أو أكثر نحصل على سطح الطبقة
يجب تحديد اتجاه القطاع ومقياس الرسم على القطاع
إذا رسم القطاع الجيولوجي في اتجاه موازي لخطوط المضرب فإن الطبقات تظهر علی القطاع الجيولوجي أفقيا، وعند رسم القطاع في هذه الحالة تتبع الخطوات السابقة من نقاط تقاطع مکاشف أسطح الطبقات مع خط البروفيل ترسم منها أسطح الطبقات من وضع أفقي
1. نرسم المقطع الطبوغرافي 2. نحدد سُمك كل طبقة ونوع الصخر الذي تحتويه – ان امكن – 3. نرسم الطبقات داخل الخريطة الطبوغرافية التي رسمناها 4. نرسم العمود الجيولوجي ونكتب بجانبه نوع الصخر وسمك الطبقات
1. تحدد على الخريطة اتجاه الشمال 2. تحدد موقع النقاط التي تريد الرسم بينها بالنسبة الى الشمال 3. تحدد الابعاد الطبوغرافية على ورقة 4. تسقط الارتفاعات المحددة على ورقة رسم بياني 5. ترسم خط بين النقاط ويجب ان لا يحتوي زواية حادة 6. تحدد تحت كل من النقطين اسفل الخريطة موقعهما بالنسبة للشمال والمسافة بينهما 7. اذا طلب منك حساب الميل تطبق القانون الموجود بالاعلى
Worksheets
Describe the landscape corresponding to the contour map (from SW to NE)Complete the contour line (CI = 10m) What is the maximum elevation?Complete the contour line (CI = 10m) What is the maximum elevation?Draw the profile (1)Draw the profile (2)Draw the profile (3)Draw the profile (4)1. What is the contour interval? 2. What is gradient between X & Y (m/km)? 3. What is the maximum elevation? 4. Draw the profile (5) between A & B
Topography is the study of geographical features on a landscape.
Topographic map is the map represent the 3D landscape of Earth within the 2D space of a map, use a colors, shading, & contour lines to represent changes in elevation, & shape
Cartographers map makers
each contour line represents an equal point of elevation, then any change in elevation would lead to inconsistent line spacing
Several contour lines spaced close together would indicate steep terrain, & lines spaced far apart would indicate gentler slope
Contour intervals the change in elevation between any two contour lines
3 kinds of contour lines
index line (I) thickest, labeled with number
Intermediate (Ln) thinner, more common, lines between the index lines, usually don’t have a number label, 1I = 5Ln
supplementary appear as dotted lines, indicating flatter terrain
Topographic Features
Peak Ring The innermost ring at the center of contour loops, represents highest elevation, & Sometimes the peak will be represented with a small X & number denoting elevation
Depression Ring an inner ring indicates a lowest elevation, which the map will show with a series of small tick marks pointing toward the center called hachures
Cliff 2 or more lines converge until they appear as a single line.
Valley (draws) When contour lines cross a valley or a stream, they make a sharp pointed V or U-shape. Rivers will run through the center of the V-shape. Sometimes called
Ridgeline like an elongated peak, not coming to a fine point. Instead of a closed inner circle, a ridgeline can look like a big oval
Saddle low lying area between 2 higher points of elevation. They appear as hourglass shapes between 2 concentric circles
Ledge Ledges or flat areas on the side of a mountain appear as protruding U-shapes that point away from the peak
Map Scales
The scale of a map is the ratio of a distance on the map to the corresponding distance on the ground
ratio scale represented as a fraction or ratio – for example 1:100 means one unit X on a map represents 100X on the surface – Ex. 1:200: 1cm on map = 200cm true
Graphic scale or bar scale – is usually printed in the lower margin of Topographic maps – bar acts as a ruler for measuring distances
Generating profiles
Draw a line between the 2 points bounding the desired profile area
Place a folded sheet of paper along the line
Mark each contour line intersecting the paper
Indicate the vertical height with a dot on a scale
Connect the height dots with a smooth line
Step 1: Draw a line between the 2 points bounding the desired profile areaStep 2 : Place a folded sheet of paper along the lineStep 3 : Mark each contour line intersecting the paperStep 4 : Indicate the vertical height with a dot on a scaleStep 5 : Connect the height dots with a smooth line
Examples
Exercises
Worksheet 1 1. The river flow in ____ Direction 2. The Sea location ______Worksheet 2 What is the elevation of points (A, B, C, D, E) Worksheet 3 Draw the topographic profile
Solutions
Worksheet 1 1. South West to North East (SW → NE) 2. North east (NE)
Worksheet 2 1.4cm → 250m 1cm → 178.6m A = 750m + (0.3cm*178.6m/cm) = 804m B = 500m + (0.7cm*178.6m/cm) = 625m C = 500 + (0.4cm*178.6m/cm) = 571m D = 250 + (0.4cm*178.6m/cm) = 321m E = 250 – (0.4cm*178.6m/cm) = 179m
are 2D map representation of 3D surface that show the location of every natural feature within the map’s area
Map Directions
Maps direction is geographic (true) north
In maps that don’t contain a direction, We always assume that the N → up on the map
Contour lines
lines on topographic maps that represent equal elevations above sea level (0), & represent 3D features on the paper
Contour Intervals The difference in elevation between 2 contour lines
Relief differences in elevation between 2 point
Index contour line between5 contour line
Map Scales
The scale of a map is the ratio of a distance on the map to the corresponding distance on the ground
ratio scale represented as a fraction or ratio – for example 1:100 means one unit X on a map represents 100X on the surface – Ex. 1:200: 1cm on map = 200cm true
Graphic scale or bar scale – is usually printed in the lower margin of Topographic maps – bar acts as a ruler for measuring distances
Reading & drawing a map
To find the elevation of a point on a map 1. The elevation can be determined directly if the point is located on contour line 2. If the point is located between contour lines, its elevation must be estimated
rules for drawing contour lines 1. Represent only one elevation 2. neverdivide or split 3. the 2 ends of a contour line must join 4. never intersect other lines 5. will bend & form a V pattern (streams) 6. Closely spaced indicate a steep slope 7. widely spaced indicate a gentle slope 7. Rings indicate mountain 8. Rings of hachured indicate a depression
Mountains → Closed contour lines (rings)Depressions → Closed contour lines (rings) are hachured include tick marks the smallest ring (lowest ring) is centermostCortoutlines that are almost parallel to one another represent slopes Steep Slopes contour lines are close together Gentle Slopes contour lines are wider apart The closer the contour lines, the steeper the slopeDirection of a stream
Examples
Worksheet 1 : Use this map to answer the following questions
Questions
1. the creek flowing ____ of Pikitigushi Lake A. into B. out
2. A creek joins Lake E from W, the creek flow ____ of Lake E? A. into B. out
3. You are walking south, from B to C, you are A. gaining elevation B. losing elevation C. remaining level
4. If You walk from B to D. You Are _____ A. going up a steep hill B. going down a gully C. going up a gully
5. You are standing at point A, What is your height above sea level?
6. You are standing at point A, What is your height above lake?
7. From B, towards Lake, Describe topograpic features between B & the lake
Worksheet 2 : Use this map to answer the following questions
Questions
1. What is the contour interval?
2. What are the small marks on the contour lines on the right side of the map called?
3. What do the small marks on the contour lines to the right indicate?
4. What is the approximate elevation of A?
5. What is the elevation of contour line B?
Solutions
Worksheet 1
1. Into (A)
2. Out (B)
3. (B > 1,350ft, C < 1,350) losing elevation (B)
4. going down a gully
5. A lacated at 1,250ft above the sea level
6. A located at 1,250ft & lake located at 950ft – both above sea level -, then elevation of point A above lake = 1,250 – 950 = 300ft above lake
7. B lacated over a mountain with elevation approximately 1360ft, and toward the lake there are GENTEL SLOPE, & then become STEEP SLOPE
The hypothesis: Supercontinent began breaking apart about 200 My ago – Continents drifted to present positions – Supercontinent called Pangaea
Pangaea, 200Ma
Evidence used in support of continental drift hypothesis
Fit of the continents, Fit of: – the shore lines – continental shelves edges at 900m depth
Fossil Distribution of fossils like Mesosaurus found in black shales of Permian age
Rock type & structural similarities Matching mountain ranges
Paleoclimatic evidence – Paleozoic 300Ma, ice sheets covered of SH, & India, & Now these are tropical & subtropical – in NH large tropical swamps existed that became major coal fields of eastern USA, Europe, & Siberia now
Rock typee & structural similaritiesfossil evidence
The Great Debate
Objections to the hypothesis – Lack of a mechanism for moving continents – Strong opposition to the hypothesis
Continental drift & the scientific method – Wegener incorrectly suggested that continents broke through the ocean crust, much like ice breakers cut through ice – Wegener’s hypothesis was correct in principle, but contained incorrect details A few scientists considered Wegener’s ideas plausible & continued the search
Plate Tectonics Theory PTT
All the following led to PTT, Oceanographic exploration after WW2, discovered:
Global oceanic ridge systems
Dredging in the seafloor didn’t bring up oceanic crust older than 180Ma
Sediment accumulations in the deep-ocean basins were found to be thin
Mid-Atlantic Ridge the youngest in red & orange, yellow, green, & older, & The blue rocks date to the Jurassic 150 -200Ma when Atlantic started to growEarth’s major plates there are 7 major lithospheric plates Plates motion & changing in shape & size Some plates include continent + seafloor Plates move at a rate 5cm/yrLithospheric plates
Part2: Plate boundaries
Plate boundaries
Interactions among individual plates occur along their boundaries
Types of plate boundariesTypes of Convergent Plate Boundaries subducting plate: The plate that slides, oldest, cooler, denser over riding plate: younger, less denseoceanic ridges: elevated areas of seafloor characterized by high heat flow & volcanism – Length 70,000km, 20% of earth surface – Width 1000 – 4000kms – Crest of ridges 2-3 km above seafloor rift-valley: deep down-faulted structure along the axis of some ridge segments
Continental rifting
splits landmasses into 2 or more smaller segments along a continental rift
Produced by extensional forces on plates
such as East African rift valleys
Ridge system & ocean basin formedif 1. Upwarping of the crust associated with mantle upwelling 2. stretching lithosphere breaks crustal rocks produced continental rift 3. Rift valley lengthens & deepens forming Linear sea
Harry Hess envisioned new sea floor being created at the mid-ocean ridge & destroyed in deep ocean trenches
Part3 :TESTING THE PLATE TECTONICS MODEL
Evidence from ocean drilling
Age of deepest sediments seafloor spreading produced by drilling ocean-floor sediment
Thickness of ocean-floor sediments verifies seafloor spreading
Hot spots & mantle plumes
Hot spot area of volcanism, high heat flow, & crustal uplift
Caused by rising plumes of mantle material Mantle plumes – Upwelling of hot rock – Some originate at great depth – perhaps at the mantle-core boundary – As hot plume ascends via mantle confining P decreases causing partial melting – This activity is seen as hot spot on surface
As Pacific plate moves over hot spot a chain of volcanic structures is built
Hawaiian Island chain showed increasing age of volcanoes towards NW
Paleomagnetism
Earth has a magnetic field similar to that produced by a simple bar magnet, & AFFECTS ALL MAGNETIC OBJECTS ON EARTH
Most Fe-bearing minerals are: – magnetic – gain magnetization below Curie point T – align themselves in the direction of the existing magnetic lines of force
Rocks that formed millions of years ago contain a “record” of the direction of the magnetic poles at the time of their formation (fossil magnetism)
Apparent polar wandering – Lava flows of different ages indicated several different paleomagnetic poles positions within the same continent – Polar wandering curves are more readily explained by the theory of plate tectonics
Magnetic surveys were also done in the ocean floor using a magnetometer
magnetometer instrument used to measure magnetic intensity
The surveys showed high & low intensity magnetic stripes within the ocean floor which are symmetrical along the opposite side of the ridges
When rocks exhibit the same magnetism as the present magnetic field, they are said to possess normal polarity. & Rocks with the opposite magnetism are said to have reversed polarity, Dates when the polarity of Earth’s magnetism changed were determined from lava flows
Magnetic reversals & seafloor spreading Earth’s magnetic field periodically reverses polarity, the N magnetic pole becomes the S, & vice versa (reversed polarity)Magnetic reversals Geomagnetic reversals are recorded in the ocean crust In 1963 Vine & Matthews tied the discovery of magnetic stripes in the ocean crust near ridges to Hess’s concept of seafloor spreading
Forces that drive plate motion
Convective flow in the mantle Slab pull Ridge push Slab suction
Is the Force exerted against a surface by the continuous collision of gas molecules
Is the P exerted by the weight of the air above
The Ρ differences causes the air to move from higher Ρ toward a region of lower Ρ
Pressure Units
At sea level: 1 atmosphere (atm) 14.7 pounds/inch² (p/in²) 101,325 Newton/m² (N/m²) 101,325 Bascal (Pa) 1013.25 millibars (mb) 29.92 inch of mercury (inHg) 760 millimeter of mercury (mmHg) 76 cm of mercury (cmHg) 760 torr
SI unit is the pascal 1 mb = 100 N/m² (Meteorologists use thies) 1 mb = 100 Pa
Bascal (Pa) is the force (1N) acting on a unit aria (1m²)
DAILY P VARIATIONS
The largest P difference, about 2.5mb, occurs near the equator
daily (diurnal) fluctuation of P are due to the absorption of solar energy by O₃ in upper atm & H₂O in lower atm
thermal tides (or atmospheric tides): The warming & cooling of the air creates density oscillations, that show up as small pressure changes near the earth’s surface
Measuring Pressure
Barometer Fluid Filled, liquid mercury Aneroid barometer No fluid, Aneroid cell RecordingBarograph An aneroid barometer, records a P over time
Why is mercury rather than water used in the barometer? convenience – Mercury seldom rises to > 80 cm – A water is 13.6 times less dense than Hg, an atm P of 76 cmHg, would be equivalent to 1034 cmH₂O – A water barometer resting on the ground near sea level would have to be read from a ladder over 10 m tall
Barometer
Influence of Τ & Water Vapor
Warm Air Faster molecules, less dense, low P Cold Air Slower molecules, denser, high P
Add H₂O makes air lighter (less Dense): Cold, & dry → Higher P, Higher ρ Warm, & dry → low P than Cold, dry Cold, & humid → less than warm & dry Warm, & humid → Lowest P, & lowest ρ cold,dry> warm,dry> cold,wet> warm,wet
Isobars A Map View of Pressure Contours lines or curves of constant P They are corrected for altitude to equivalent Sea Level Pressure (SLP)
Pressure & Wind
Wind is nature’s attempt at balancing inequalities in pressure – Unequal heating generates inequalities in P
Winds flow from high to low pressure
Wind caused by → Solar radiation (SR) is the source of energy → SR causing differences in heating (O₃ absorb it in upper atm, & H₂O in lawer) → Unequal heating causes horizontal differences in pressure HDP → HDP cause PGF (causes wind to start move) → the wind flow from region of high P to regions of low P under PGF due to HDP
Main forces that affect wind 1. Pressure Gradient Force (PGF) 2. Coriolis Force (rotation of the Earth) 3. Centripetal force 4. Friction 5. Gravity
2 forces cause wind speed & direction to be different than predicted by the PGF 1. Coriolis (rotation of the Earth) 2. Friction
Wind flow in a straight line from high to low P If Earth didn’t rotate & there was no friction
Winds flow from High to Low P if affected by HPD that caused PGF
The gas law: P α (ρ x Τ) PV = nRT → P = (mRT)/VMw P = (ρRT)/Mw → P α (ρ x Τ)
Winds flow from High to Low P if affected by Horizontal Pressure Differences (HPD)Change in P over large distance = small PGF Change in P over small distance = large PGFPGF & Isobars PGF is at right angles to isobars
PGF STRONGER if isobars are closer together
When given P Heights, the PGF points from regions of High P to that of Low P
If all we had was the PGF, wind would act like a Ball rolling down a slope… rolling at 90° to the slope!
Coriolis Force Fc
Results from the rotation of the Earth – Earth rotates 15°/hr
Causes PGF to cross isobars not at right θ – Winds curve to the RIGHT in the NH – Winds curve to the LEFT in the SH
Affects wind direction, not speed
Affected by(factors determine the magnitude of the Coriolis Force) 1. wind speed – Stronger wind → greater force 2. latitude dependent – Strongest at the poles – nonexistent at the equator
On a non‐rotating Earth, the rocket would travel straight to it’s target
Even though the rock travels in STRAIGHT line, when we plot it’s path on the surface it follows a path that CURVES to the RIGHT!Coriolis Force FcGeostrophic Flow: winds run parallel to isobars in a straight path if – only the PGF & Fc affect an air parcel – air parcel is at equilibrium, if PGF & Fc opposite in directionCurved Flow: wind that follow curved paths around high & low pressure cells
Speed of the wind depends on how close is the isobars are
Friction
Applied to wind within 1 to 1.5 km of the surface
direction of Friction – direction always opposite of motion – direction towards of the PGF – direction of the low P – direction opposite of the Fc
affects air at the surface more than air aloft (decreases with hight)
Combining the forces Geostrophic Flow & Friction together causes parcel to slow down Fc decreases in strength
Vertical Motion & Pressure
Movement of air can cause variations in P Net flow of air into a region = CONVERGENCE Net flow of air out of a region = DIVERGENCE
If a cloud droplet is in equilibrium with its surroundings its size doesn’t change because rate of condensing onto the droplet = rate of evaporating from it
If cloud droplet is not in equilibrium its size – increase if condensation > evaporation – decrease if condensation < evaporation
To keep the droplet in equilibrium more vapor molecules are needed around it, to replace molecules that evaporating from it
In equilibrium, The total number of vapor molecules around the droplet remains constant & defines the droplet’s saturation vapor pressure
equilibrium vapor pressure is the saturation vapor pressure at equilibrium
a Cloud droplet is 100 times smaller than a raindrop Cloud drops are VERY TINY (0.02 mm) Rain drops are VERY BIG (2 mm)
curvature effect
When air is saturated with respect to a flat surface, it is unsaturated with respect to a curved droplet (Evaporate)
As a result of curvature effect to keep smaller cloud droplets in equilibrium → smaller droplets has greater curvature → so more rapid rate of evaporation → so require greater vapor pressure → The air must be supersaturated (RH>100%)
since the smaller nuclei are more affected by curvature effect, only the larger nuclei are able to become cloud droplets
Reason is the water molecules are less strongly attached to a curved water surface, they evaporate more readilycurvature effect The evaporation over a flat surface of water is less than evaporation of same amount of water over a curved surface
Solute Effect
Condensation begins on tiny particles called cloud condensation nuclei (CCN)
Hygroscopic particles: type of CCN, have an affinity for H₂O, & Condensation begin on it when the RH < 100%, such as salt particles
Salt are dissolve in water forming solution & the salt ions in solution bind closely with H₂O so preventing it from evaporate
solute effect: reduces the equilibrium vapor pressure, by strong association of hygroscopic molecules with water in solution
Due to the solute effect: 1. the salt replaces H₂O in lattice structure 2. the equilibrium vapor pressure is lowered
droplet containing salt can be in equilibrium when the RH << 100%
Should RH increase: → water vapor molecules would attach to the droplet at a faster rate than they would leave →the droplet would grow larger in size
Condensation in Unsaturated air
In moist but unsaturated air: – condensation occurs as air cools, RH ≈78 – As the air cools further, RH increases, with the droplets containing the most salt reaching the largest sizes.
Over land masses where large concentrations of nuclei exist, several hundreds/cm³, all competing for the available supply of H₂O(g)
Over the oceans where the concentration of nuclei is less, < 100/cm³, but larger cloud droplets
So, in a given volume we tend to find 1. more cloud droplets in clouds over land 2. larger cloud droplets over the ocean
processes of rain produced
Collision‐Coalescence process Bergeron: the ice‐crystal process
COLLISION & COALESCENCE PROCESS
Air retards the falling drops
The amount of air resistance depends on: 1. rate of fall 2. The size: larger fall faster! 3. Speed: mire speed → more air encounters 4. Coalescence: Large droplets collide & merging with smaller drops in their path
Terminal Velocity: constant speed of falling drop if the air resistance =F.gravity – The speed of the falling drop increases until the air resistance equals the pull of gravity
larger drops fall faster than smaller drop larger drops have a smaller surface area to weight ratio, they fall faster before reaching their terminal velocity
Coalescence enhanced if colliding droplets have opposite & attractive electrical charges
Rising air currents in a forming cloud, slow the rate of fall toward the ground
amount of time the droplet spends in the cloud An important factor influencing cloud droplet growth by the collision process
Thick cloud with strong updrafts maximizes 1. the time cloud droplets spend in the cloud 2. the size to which they can grow
In warm cloud composed of small droplets of uniform size, the droplets are less likely to collide as they all fall very slowly at about the same speed, droplets that do collide, do not coalesce because of the strong surface tension that holds together each tiny droplet
In a cloud composed of droplets of varying sizes, larger droplets fall faster than smaller droplets. Although some tiny droplets are swept aside, some collect on the larger forward edge, while others (captured in the wake of the larger droplet) coalesce on the droplet’s back sidewarm rain Rain that falls from warm clouds The most important factor in the production of raindrops is the cloud’s liquid water content.
In a cloud with sufficient water, other significant factors are: 1. the range of droplet sizes 2. the cloud thickness 3. the updrafts of the cloud 4. the electric charge of the droplets and the electric field in the cloud
Bergeron Process
process of ice crystal growth that occurs in mixed phase clouds (containing a mixture of supercooled water and ice) in regions where the ambient vapor pressure falls between the saturation vapor pressure over water and the lower saturation vapor pressure over ice.
This is a subsaturated environment for liquid water but a supersaturated environment for ice resulting in rapid evaporation of liquid water and rapid ice crystal growth through vapor deposition
Precipitation in Cold Clouds
Ice, water & water vapor exist at the same time
Cloud drops DON’T FREEZE at 0°C
Liquid water won’t freeze until ‐40C°, SUPERCOOLED
Supercooled water freezes when it touches a Freezing Nuclei, FN are rare
ICE-CRYSTAL PROCESS
The ice‐crystal (or Bergeron) process of rain formation is extremely important in middle and high latitudes, where clouds extend upward into regions where the air temperature is well below freezing.
Such clouds are called cold clouds.
a typical cold cloud that has formed over the Great Plains, where the “cold” part is well above the 0°C isothermEventually the ice crystals will grow large enough to fall. The Bergeron Process often results in liquid precipitation. As the crystals grow and fall, they pass through the base of the cloud, which may be above freezing. This causes the crystals to melt and fall as rain.
The Bergeron Process Summary
The air reaches saturation and some of the resulting droplets will come in contact with freezing nuclei (assuming they have reached the activation temperature).
There is then a combination of ice crystals and supercooled water droplets.
From the perspective of the supercooled droplets, the air is in equilibrium at saturation, but from the perspective of the ice crystals, the air is supersaturated.
water vapor will sublimate on the ice crystals. Since the amount of water vapor in the air has decreased, and from the perspective of the supercooled water droplet, the air is subsaturated, the supercooled water will evaporate until the air once again reaches saturation.
The process then continues.
In short summary, the ice crystal grows through sublimation at the expense of the supercooled water droplet.
Precipitation in Warm Clouds
In warm clouds there are no Ice Crystals so the Bergeron Process can’t operate
Collision‐Coalescence a.k.a. Bump & Stick
Need one BIGGER than average Cloud Drop
Really large aerosol (CCN) → Start Big…. End Big
Entrainment Mixing (evaporation & redistribution)
Turbulence (smashing together of droplets)
Collision-Coalescence
Terminal Velocity matters
the highest velocity attainable by an object as it falls through the air
Sum of the drag force and buoyancyequals the downward force of gravity
If cloud drops were all the same size could they bump into each other? NO
BIG drops fall FASTER than SMALL drops!!!
How ice crystals grow & produce precipitation in clouds with a low H₂O(ι) content & a high H₂O(ι) content
Cloud Seeding & Precipitation
The primary goal in many cloud seeding experiments is to inject (or seed) a cloud with small particles that will act as nuclei, so that the cloud particles will grow large enough to fall to the surface as precipitation.
Some of the first experiments in cloud seeding were conducted by Vincent Schaefer & Irving Langmuir during the late 1940s.
To seed a cloud, they dropped crushed pellets of dry ice (solid carbon dioxide) from a plane. Because dry ice has a temperature of ‐78°C (‐108°F), it acts as a cooling agent.
“Fake Ice” to simulate the Bergeron Process (Dry Ice, Silver Iodide)
In 1947, Bernard Vonnegut demonstrated that silver iodide (AgI) could be used as a cloud‐ seeding agent.
Because silver iodide has a crystalline structure similar to an ice crystal, it acts as an effective ice nucleus at temperatures of ‐4°C (25°F) & lower.
Silver iodide causes ice crystals to form in two primary ways: 1. Ice crystals form when silver iodide crystals come in contact with supercooled liquid droplets. 2. Ice crystals grow in size as water vapor deposits onto the silver iodide crystal.
Cloud Seeding & Precipitation
Hard to “prove” that it actually worked.
Need the right ratio of cloud droplets to ice crystals.
Concern over toxicity of silver iodide.
You can “overseed” a cloud and too many ice crystals are formed so it doesn’t rain
You can also “overseed” cold fog with dry ice to dissipate it.
Forms of Precipitation
Snow & Hail is seen on Big Island Sleet, Glaze, & Rime do not seen on Big Island
Rain
Drops of water that fall from a cloud & have a diameter of at least 0.5mm
atm is warm, above freezing, from the surface to the cloud layer (Hits the surface as a liquid)
Rain can start out as an ice crystal (Bergeron) or as a large droplet (Collision‐ Coalescence)
DRIZZLE & MIST: Small drops
Virga: Rain that evaporates before reaching the surface
Flooding, Flash Flood
Atmospheric Profile for Rain
Snow
Ice crystals & clumps
atm is cold, below freezing, from the surface to the cloud layer (Hits the surface as solid ice)
Snow will start out as ice crystal (Bergeron)
Very Cold Conditions – light snow: Individual crystals
Warmer Cold Conditions – wet snow: Crystals form clumps
Atmospheric Profile for Snow
Sleet
Rain that freezes near the surface, Wintertime phenomenon
atm is cold, below freezing, in the cloud layer & at the surface, & there is a layer in between that is above freezing
(Hits the surface as solid ice pellets) Precipitation (from snow) → rain → sleet
Clearto translucent pellets (Ice Pellets)
Atmospheric Profile for Sleet
Freezing Rain & Glaze
Rain falls in liquid & then freezes at ground
atm is cold (below freezing) in the cloud, above the surface there is a warm (above freezing) layer than melts the snow.
just at the surface there is a layer of below freezing that causes the rain drop to freeze on contact with the surface
Glaze The coating of ice
Profile for Freezing Rain
Hail
Rounded WHITISH Pellets & Irregular lumps of ice, 1‐5 cm & Can weigh > pound
Can be very destructive & damage cars, crops, & even kill people!
The hail Formation Produced in a Cumulonimbus cloud Graupleor large frozen rain dropsact as embryos
They accumulate supercooled water, adding new layer
Violent, upsurging air currents within the storm carry these embryos up via the cloud
Low liquid water makes a white layer Higher liquid water makes a clear layer
When the updraft can no longer keep it aloftit falls to the surface
The more violent the storm the larger the hail can become.
Rime
This is a deposit of ice crystals
Formed by freezing of supercooled fog or cloud droplets on objects whose surface is below freezing
External Processes: Occur at or near Earth’s surface, Weathering, Masswasting, & Erosion Internal processes: derive their energy from Earth’s interior, Mountain Building & Volcanic Activity
Mass Wasting
is the downslope movement of rock & soil due to gravity Controls & triggers of mass wasting: 1. Water: Reduces the internal resistance of materials & adds weight to a slope 2. Oversteepening of slopes 3. Removal of vegetation: Root systems bind soil & regolith together 4. Earthquakes &aftershocks: dislodge large volumes of rock & unconsolidated material
Mass Wasting Types
Slide material contact with the surface – It can preserve its form or deformed – include 1. Rock slides or land slides translation movement along a planer surface 2. Slump rotational along concave surface
Fall free fall, looses contact with surface
Flow movement of unconsolated material saturated with H₂O with other behaving in a plastic to liquid manner, contact with surface – Individual particles get rearranged – include 1. Dibri flow (or solifluction flow) 2. Earth flow 3. Mud flow
Water Cycle
is a circulation of Earth’s water Processes in the water cycle Precipitation Water returns to earth Evaporation transfer from liquid to solid Infiltration water absorption by Rock & soil Runoff Water returns to water bodies Evapotranspiration Evaporation by plants Sublimation: transfer from the gaseous state of the solid or liquid Condinsation forms clouds In hydrologic cycle output = input, rate of Evaporation = rate of preciptationWater distripution at the earth surface
Running Water
Stream flow
Stream water running in a channel The ability of a stream to erode & transport materials is determined by velocity Factors that determine velocity 1. Gradient, or slope: vertical drop of a stream over a specified horizontal distance 2. Discharge: The volume of water moving past a given point in a certain amount of time 2. Channel characteristics: – Shape: V-shaped (up) & Semicircle (down) – size: directly proporational to velocity – roughness: inversaly proporational to velocity
Profile Cross-sectional, view of stream headwaters(source) Viewed from the head, to mouth of a stream Up stream (Head) law velocity, law discharge, small size, steep gradient, V-shaped, & Rough Down stream (Mouth) high velocity, high discharge, large size, gentle gradient, semicircle, smooth curve
Drainage basins & pattern
Drainages
Drainage Basins: Drainage networks, land area that contributes water to the stream Drainage pattern: interconnected network Drainage Basins include Tributary, River, Delta, & Ocean divide: Imaginary line separating one basin from another
divided in 3 zones based on the dominent processes operating within them: 1. Zone of Sediment Production 2. Zone of Sediment Transport 3. Zone of Sediment Deposition
Base Level
Base level: is the lowest point to which a stream can erode Two general types of base level 1. Ultimate (sea level) 2. Local (temporary) There are 2 forms of river erosion 1. Down cutting esosion 2. Lateral esosion Changing conditions causes readjustment of stream activities 1. Raising base level causes deposition (decreasing in velocity & Gradient) 2. Lowering base level causes erosion (increasing in velocity & Gradient)
Adjustment of Base Level to Changing Conditions
The Work of Streams
Stream erosion
Lifting loosely consolidated particles Abrasion & Dissolution Potholes formed when a strong current moves large paticles
Potholes in channel floor
Transport of sediment by streams
stream’s load Transported material Types of load 1. Dissolved load (in solution) 115-120 ppm 2. Suspended load (silt & clay) 3. Bed load (down cutting of stream) Competence the max. particle size stream can transport, Determined by the stream’s velocity Capacity the max. load a stream can transport per time, increases with discharge
Deposition of sediment by a stream
Caused by a decrease in velocity – Competence is reduced – Sediment begins to drop out,each particle size has a critical settling velocity – Solid particle of various size separated(sorting) Stream sediments(alluvium) well sorted
Stream channels
Bedrock channels found in headwaters, steep gradient, V-shaped, rivers cut into bedrock. Waterfalls & pot holes are usually seen Alluvial channels composed of loosely consolidated sediment (alluvium)
2 types of Alluvial channels
Meandering: move in sweeping bends, found in downstream, becomes mendering because if lateral erosion Braided consist of network of converging & diverging channels (load consists of coarse material & the stream has high discharge)
Meandering channels Braided channels
Forms of deposition of sediments by streams
Delta Body of sediment where a stream enters a lake or the ocean Natural leveesForm parallel to the stream channel by successive floods over many years Floodplain deposits
Delta Results from a sudden decrease in velocity Natural leveesFormation of Natural Levees Formation of Back swamps Yazoo tributaries
Stream Valleys
Common landforms on Earth’s surface Two general types of stream valleys 1. Narrow valleys – V-shaped – Downcutting toward base level – Features often include rapids & waterfalls 2. Wide valleys – Stream is near base level – Downward erosion is less dominant – Stream energy is directed from side to side – forming a floodplain Features of wide valleys often include – Floodplains – Meanders – Cut banks & point bars – Cutoffs & oxbow lakes
Erosion & Deposition Along a Meandering Stream
Floods & Flood Control
Floods are the most destructive hazard Causes of flooding Result from naturally occurring & human induced factors Causes include – heavy rains – rapid snow melt – dam failure – topography, & surface conditions Flood control 1. Engineering efforts: Artificial levees, Flood control dams, & Channelization 2. floodplain management Nonstructural approach
Water Beneath the Surface
freshwater
Largest freshwater reservoir for humans Geological roles 1. erosional agent, dissolving by groundwater produces: Sinkholes, & Caverns 2. An equalizer of stream flow
Distribution of groundwater
Belt of soil moisture – Zone of aeration – Unsaturated zone – Pore spaces of material are filled with air Zone of saturation – All pore spaces of material filled with H₂O – Water within the pores is groundwater Water table upper limit of zone of saturation
Groundwater provides streams with water
Movement of groundwater
Porosity Percentage of pore spaces to the total volume of the rock. – determines how much groundwater can be stored Permeability Ability to transmit water via connected pore spaces – Pores must be connected & large enough to allow movement Aquitard impermeable layer of material (clay) Aquifer permeable layer of material (sand & gravel) confined aquifer confined between 2 aquitard unconfined aquifer water table forms the upper boundary
Springs
Whenever the water table intersects surface Hot springs – Water 6 – 9ºC warmer than air temperature – depth increase of temperature by 2°C/100m – Heated by cooling of igneous rock Geysers – Intermittent hot springs in which columns of water are ejected with great force at various intervals – Water turns to steam & erupts – occur where extensive underground chambers exist within hot igneous rocks – At the bottom of the chamber, the water is under great pressure preventing water from boiling at 100°C
Wells
Well a hole bored in the zone of saturation to remove groundwater Artesian Wells Water in the well rises higher than the initial groundwater level – Artesian wells act as “natural pipelines” moving water from remote areas of recharge great distances to the points of discharge
Formation of a Cone of Depression Pumping cause a drawdown (lowering) & a cone of depression in the water tableAn Artesian Well Resulting from an Inclined Aquifer
Environmental problems associated with groundwater
– Treating it as a nonrenewable resource – Land subsidence caused by its withdrawal Contamination
Geologic work of groundwater
dissolves rock Groundwater if often mildly acidic Contains weak carbonic acid CaCO₃ + H₂CO₃ → Ca⁺ + 2HCO₃- Calcite → bicarbonate ion carried away in solution Dissolves calcite in limestone
Caverns Formed by dissolving rock beneath Earth’s surface, in the zone of saturation – Composed of dripstone – Calcite deposited as dripping H₂O evaporates Features found within caverns 1. Stalactites hanging from the ceiling 2. Stalagmites (dripstones) growing upward from the floor
Karst topography
Formed by dissolving rocks at or near surface Area lacks good surface drainage Common features 1. Sinkholes Surface depressions, form by dissolving bedrock & cavern collapse 2. Caves & caverns
Important terms
Groundwater is the largest reservoir of fresh water that is readily available to human. Zone of aeration underground area above water table, is not fully saturated with water Zone of saturation underground area below the water table in which the pore spaces are fully saturated with water Water table surface that separates zone of aeration, from underlying zone of saturation Porosity the proportion of open spaces (or pores) in sediment or rock, expressed as the percent of voids to the total rock volume Aquifer a permeable layer of sediment or rock from which water can be obtained spring is a naturally occurring intersection of the water table with the surface of the ground from which water flows spontaneously A well is an opening bored down into the zone of saturation and into a confined aquifer Overpumping resulting in – cone of depression around the pumping well – intrusion of salt water into freshwater well – land subsidence – causing damage to an aquifer resulting in such a significant water level decline Permeability Ability to transmit water via connected pore spaces Porosity Percentage of pore spaces to the total volume of the rock. Drainage basin land area that contributes water to a stream Divide imaginary line which separates drainage basins Gradient the slope of stream channel expressed as the vertical drop of a stream over a specified distance Discharge the volume of water flowing past a certain point in a given unit of time base level is a lower limit to how deep a stream can erode Meandering river generally move in a sweeping bends Cutoff the new & shorter channel segment of meandering river, is for the outer edge of a meander, because of its shape called Oxbow Delta may form where a river deposits sediments in another water body at its mouth Naturallevees result from sediment deposited along the margins of a stream channel by many flooding events streams transport load of sediments in : 1. solution (dissolved particles) 2. suspension 3. along the bottom of the channel (Bed load)
The rock cycle describes the interactions between the components of the Earth system Origin of igneous, sedimentary, & metamorphic rocks & how they connected Any rock can be transformed into any other rock type under the right conditions
The rock cycle
The rock cycle begins with magma Forms from melting in crust & mantle Less dense magma rises toward the surface Erupts at surface as lava, cools within crust
Magma: generated by melting in the mantle, & some by melting the crust, & Rises because it is less dense than surrounding rock
lava: Magma reaches Earth’s surface
Cooling is crystallization or solidification
Igneous rocks are crystallized from – Magma: within the crust – lava: at Earth’s surface Igneous rocks exposed at Earth’s surface undergo weathering Atmosphere decomposes rock Generates loose material or dissolves it
Loose material is called sediment Transported by gravity, running water, glaciers, wind, waves, etc. Most sediment is transported to the ocean, but some is deposited in other environments
lithification: Deposited sediment “conversion into rock” by Compaction & Cemention
Metamorphism: Deformed by great heat & pressure if deeply buried or incorporated into a mountain chain
heat can melt the rock & generate magma
Rocks aren’t stable unchanging masses over geologic time scales, & Rock cycle happens over millions or billions of years
Different stages of the rock cycle are occurring today all over Earth’s surface – New igneous rocks are forming in Hawaii – The Colorado Rockies are eroding & material is being carried to the Gulf of Mexico
Rocks don’t always go through the rock cycle from igneous to sedimentary to metamorphic – Igneous remain deeply buried & become metamorphosed – Sedimentary & metamorphic uplifted & eroded into sediment instead of melted
The rock cycle is driven by internal heat & external processes (weathering & erosion)
Processes for transform a rock – Igneous form if molten magma crystallizes – Sedimentary form if weathered particles are lithified (compaction & cementation) – Metamorphic rocks form when other rocks are exposed to heat & pressure
Igneous Rocks
Formed by Fire, form when magma or lava cools & crystallizes
extrusive or volcanic rocks: Solidification of lava at Earth’s surface – Abundant in the NW (Cascades, Columbia) – Many oceanic islands are volcanic (Hawaii) Most volcanic eruptions are not violent
intrusive or plutonic rocks: magma never reaches the surface, & solidifies Exposed at the surface by uplift & erosion – Mount Washington (New Hampshire) – Stone Mountain (Georgia) – Mount Rushmore & Black Hills (S-Dakota) – Yosemite National Park (California)
Magma contains ions (Si, O) & gas (H₂O) confined by pressure, & solid crystals
Crystallization occurs as mobile ions arrange into orderly patterns during cooling
As cooling continues, more ions are added to the crystals until all of the liquid becomes a solid mass of interlocking crystals
Igneous classified by Texture: results from cooling history, interloking texture Mineral composition: derives from parent magma & environment of crystallization
The texture
described based on size, shape, & arrangement of grains
Used to make inferences about rock’s origin Large crystals → slow cooling → common in magma chambers deep in the crust Fine-grained → rapid cooling → at the surface or in small masses in the upper crust – crystals small to see with the naked eye vesicular voids left by gas bubbles that remained when lava solidified (scoria) Coarse-grained →Solidified at depth while insulated by surrounding rock – Masses of interlocking crystals roughly the same size (large to be seen by the naked eye) Porphyritic Large crystals in matrix of smaller crystals Different minerals crystallize under different T-P conditions & One mineral can reach large size before other minerals start to form Glassy texture when rocks cool rapidly Atoms freeze in place before they can arrange themselves in an orderly structure More likely in silica-rich magmas Form during volcanic eruptions
Composition
Igneous rocks mainly composed of silicate Si & O + (Al, Ca, Na, K, Mg, Fe) make up 98% of most magmas, & includes small amounts of trace elements Ti, Mn, Au, Ag, U During crystallization, these elements combine to form 2 major groups of silicate Dark silicates: rich in Fe & Mg, low in Si such as Olivine, pyroxene, amphibole, biotite Light silicates contain Na, K, Ca, richer in Si such as Quartz, mica, feldspars Feldspars are most abundant mineral group 40% of most igneous rocks
Crystallization influenced by Magma composition Dissolved gas Rate of cooling – Slow cooling → fewer, large crystals – Quick cooling → tiny intergrown crystals – Instantaneous cooling → randomlydistributed atoms, no crystal growth (formation of volcanic glass)
Volcanic ash: tiny shards of glass
Magma can evolve Different rock generated from the same melt Bowen’s reaction series describes which minerals solidify at specific T First crystallize olivine, pyroxene, plagioclase at intermediate T: Amphibole & biotite during late cooling: Muscovite & K-feldspar last to solidify: Quartz Minerals that form in the same T range tend to be associated in the same igneous rocksGranitic (felsic) rocks Igneous rocks of granitic composition made up almost entirely of light-colored silicates Quartz + potassium feldspar Felsic = feldspar + silica Most contain 10% dark silicate minerals Biotite mica, amphibole, 70% silica Major constituent of continental crust Granite: coarse-grained rock Forms when magma solidified slowly at depth, & Uplifted during mountain building Rhyolite: extrusive equivalent of granite Light-colored silicates, buff, pink, or grey Contains voids & fragments of volcanic glass Cooled rapidly at Earth’s surface Obsidian: natural volcanic glass Dark in color (metallic ions) & high Si content Chemical composition is similar to light-colored rocks Pumice: vesicular volcanic glass Gas escape from lava forms a frothy, gray Many float in water because of vesicles
Basaltic (mafic) rocks Contain substantial dark silicate minerals & Ca-rich plagioclase but no quartz Mafic = Mg + ferrum (Fe) Darker & denser than granitic because of Fe Basalt: Most common extrusive rock Dark green to black, fine-grained Contains pyroxene, olivine, & plagioclase Relatively common at Earth’s surface Volcanic islands (e.g., Hawaii, Iceland) Upper layers of the oceanic crust Central Oregon & Washington Gabbro: coarse-grained intrusive equivalent Not commonly exposed at Earth’s surface Significant component of oceanic crust
Andesitic (intermediate) between granitic & basaltic composition Mixture of both light & dark colored mineral Amphibole & plagioclase feldspar Associated with volcanic activity at continental margins diorite: Coarse-grained intrusive equivalent
Ultramafic rocks Contain mostly dark-colored minerals Olivine and pyroxene e.g., peridotite & dunite Rare at Earth’s surface Main constituent of upper mantleMagmatic differentiation formation of one or more secondary magmas from a single parent magma Explains diversity of igneous rocks Magma composition continually changes during cooling As crystals form, certain elements selectively removed, resulting in depleted magma
Crystal settlingoccurs when dense minerals sink to the bottom of a magma chamberSummary Classification of igneous rocks depend on Crystal size: Coarse, Fine, Porphyritic, Glassy, & Vesicular Composition: Granitic (felsic), Basaltic (mafic), Andesitic (intermediate), Ultramafic
Size of crystals related to cooling rate Larger crystals indicate slower cooling Smaller crystals indicate fast cooling
Sediments
Weathering & Erosion
Weathering break down of rocks, transformation of rock to reach equilibrium with environment, form Sediment – Natural response of materials to a new environment – Generally occur simultaneously
2 basic categories of weathering mechanical (physical) process of breaking down rocks into smaller pieces, Each piece retains same physical properties of original material & increases surface area chemical alters internal structure of minerals, Elements are removed or added
How does mechanical weathering break rocks? 1. Break into smaller pieces but chemical composition does not change 2. Increases surface area for chemical weathering
How does chemical break rocks down? 1. Oxidation or dissolution by carbonic acid 2. changes mineral’s crystalline structure
Erosion transports weathered rock
Mechanical weathering Increases surface area available for chemical weatheringFrost wedging (Mechanical weathering) occurs when water fills cracks in rocks & expands, & Ice expands 9% when it freezes Most pronounced in mountainous regions in middle-latitudesSheeting (Mechanical weathering) occurs when entire slabs of intrusive igneous rock break loose, Removal of overlying rock reduces pressure & outer layers expand & separate Exfoliation Domes occure due to Continued weathering (release pressure) Biological activity (Mechanical) breaks rocks apart Roots grow into cracks & wedge rock apart, & Burrowing animals expose rock to increased weatheringchemical weathering rock is transformed into new stable material Oxidation Oxygen dissolved in water carbonic acid CO₂ dissolved in water, & Abundant at Earth’s surface, & Interaction with minerals changes their structure Feldspar are broken down into clay minerals Silica is carried away by ground water Quartz is very resistant to weathering
Sedimentary Rocks: Compacted and Cemented Sediment
form after weathering breaks rocks down, gravity & erosional agents transport & deposit the sediment, & then sediment lithified
Most sedimentary rock is deposited by solid material settling out of a fluid
Sedimentary rocks make up: 5% of Earth’s outer 10 miles g 75% of all continental rock outcrops
Used to reconstruct details about Earth’s history
Economically important: Coal, Petroleum, Gas, Metals, Fertilizer, & Construction Materials
Classification
classified in 2 groups Detrital from weathered solid particle (rock) Chemical from ion in solution biochemical considered a type of chemical, Materials precipitated by organisms
Detrital sedimentary rocks Contain variety of minerals & rock fragments Clay & quartz are most common classified by particle size & then composition Used to determin environment of deposition:Higher energy → larger particles
Sandstone (or Quartz Sandsotne) Arkosic Sandsotne high Quartz Arkose > 25% feldspare, so has pink color Black Shale (organic) organic materials Red Shale has Fe-oxides White Shale
Characteristic properties of Shale is fissile (occur in weakness zone)Chemical sedimentary rocks Solid material precipitates to form sediments Ex. salt left behind when water evaporates
biochemical sediments Eg. shells & hard parts Limestone is composed of calcite CaCO₃, Nearly 90% is formed by organisms
Coquina: loosely cemented shell fragments Chalk: hard parts of microscopic organisms Travertine: inorganic limestone, in caves Chert, jasper, agate: microcrystalline SiO₂ Salt & gypsum: in evaporite deposits Coal consists mostly of organic matter, found in swamps
Formation of coal Plants buried → O, H, N in organic mater volatile so its evaporating under pressure (green color)→ beat → brown leginite → Black Petuminas (high pressure & Energy) → Anthrasite (Non sedimentary)
Lithification Process
process by which sediment is transformed into sedimentary rock, include: 1. Compaction occurs when grains are pressed closer together so that pore space is reduced – Weight of accumulated sediment – Most significant in fine-grained rocks 2. Cementation occurs when water containing dissolved minerals moves through pores – Cement precipitates, fills pores, & joins particles together – common cements: Calcite, Silica, & Fe-oxide
Characteristic of sedimentary rocks
Strata or Beds layers of sedimentary rocks Thickness range [microscopic – tens m] Mark the end of one episode of sedimentation & the beginning of another
Fossils Traces or remains of life Important clues of ancient environment Can be used to match up rocks of the same age found in different places
Metamorphic Rocks: New from Old
produced when preexisting parent rock is transformed Parent rock: can be Igneous, Sedimentary, or Metamorphic rocks
Metamorphism
Elevated T & P, occurs if rock is subjected to a different environments, Equilibrium with new environment
Most metamorphism occurs in 2 settings: 1. Contact or thermal: Rock T increases because of intruding magma 2. Regional: P & T, during mountain building, produce most of metamorphic rocks
What causes metamorphism: occurs because parent rock is not in equilibrium
How does metamorphism affect rocks: Heat & pressure change texture, mineralogy, & sometimes chemical composition
Metamorphism can change the texture Low-grade (Contact) compact, & denser High-grade (Regional) recrystallization & growth of visible crystals
Metamorphism progresses incrementally Low-grade (slight changes) to high-grade (substantial changes)
Agents of metamorphism
Heat: from intrusion of magma or burial, reactions & recrystallization of new minerals Confining pressure (contact): equal in all directions due to burial, Compaction & recrystallization Differential stress (regional):greater in one direction due to mountain building, Deformation & development of metamorphic textures – Rocks can react by breaking (brittle) – Rocks can react by bending (ductile) – brittle Vs ductile: depending on T Chemically active fluids: hydrothermal fluid rich in Fe, Catalyze recrystallization reactions – Dissolve mineral from one area & precipitate it in another, & change composition of surrounding rocks
Foliation development of a flat arrangement of mineral grains
Classification
Foliation rocks (regional) – Driven by compressional stress – Causes grains to develop parallel alignment – Includes: 1. Parallel alignment of micas 2. Parallel alignment of flattened pebbles 3. Separation of light & dark minerals 4. Development of rock cleavage
Nonfoliatedrocks – occur when deformation is minimal & parent rock is composed largely of stable minerals
Common foliated metamorphic rocks Slate hasspecial cleavage, From shale or ash Phyllite larger grains than slate, which give it a glossy sheen & wavy surface Schist formed by regional mata. of shale Gneiss banded rock that, have intricate folds Common nonfoliated metamorphic rocks Marble coarse crystalline, From limestone Quartzite very hard due to quartz grains, From metamorphosed quartz sandstone
From Slate to Gneiss (grade increase)
Summary
Foliated regional, High-grade, Differential P Nonfoliated Contact, Low-grade, Confining P
Minerals:Naturally occurring, inorganic, solid with crystalline structure & defined chemical & physical properties that allow it for some variation
Naturally occurring: Form by natural geologic processes, so Synthetic materials are not considered minerals
Inorganic: Crystalline solids from organic sources are not minerals Some organisms secrete inorganic compounds like calcium carbonate, these material considered a mineral if they become part of the rock record
Solid exception is mercury –> liquid
Crystalline structure Atoms arranged in an organized, & repetitive manner, Organization is reflected in the crystal shape
Chemical composition that allows for some variation: Most minerals are compounds so can be expressed as a chemical formula such as quartz SiO₂ – Composition vary due to substitute for elements & substituting of elements have the same size will not change the crystalline structure of the mineral
Important in human history 1. Flint & chert for weapons & tools 2. Gold, silver, & copper mined by Egyptians 3. Bronze developed by 2200 BC 4. Mining became common by Middle Ages
Crystalline structure
rocks
naturally occurring solid aggregate mass of mineral, or mineral-like matter
Most aggregates of several different minerals
Individual properties of the minerals are retained
Some rocks are composed of a single mineral, Such as limestone → calcite
Some rocks made of non-mineral, Such as obsidian & pumice (glass), & coal (organic)
Atoms
Building Blocks of Minerals
All matter, including minerals, is composed of atoms, & All atoms (excluding H & He) formed inside massive stars by fusion
Atom:the smallest particle that cannot be chemically split
particles that make up an atoms Atoms contain even smaller particles: Protons, Neutrons, & Electrons
Protons, Neutrons, & Electrons
Protons & neutrons have almost identical masses, & Electrons are much smaller (1/2000) than protons & neutrons
Protons +ve Found in the nucleus atomic number: number of P⁺ in the nucleus, & Determines chemical nature of atom element: atom with the same atomic number
Electrons– ve Surround the nucleus like a cloud Valence electrons interact to form bonds Move around the nucleus in a cloud with different regions called principle shells Each principle shell has an energy level & a specific number of electrons The outer shell contains valence electrons Interact with valence electrons of other atoms to form chemical bonds
Neutronsno charge Found in the nucleus
Most matter is neutral, because the charges of P⁺ & e- cancel each other out
e- are sometimes shown orbiting the nucleus like planets in a solar system, & actually surround the nucleus like a cloudApproximately 90 naturally occurring elements Elements are arranged in the periodic table Elements with similar properties line up in columnsMost minerals are chemical compounds 2 or more elements joined together, A few minerals are made up of single elements Native minerals
Atoms Bond
Elements (excluding noble gasses) form bonds under the T & P conditions that occur on Earth Bonds lower the total energy of the atoms & make them more stable
The Octet Rule Atoms tend to gain, lose, or share electrons until they have eight valence electrons
Eight valence electrons is a stable arrangement & a full valence shell
The noble gasses all have full valence shells so they lack chemical reactivity
Elements gain, lose, or share electrons during chemical reactions producing stable electron arrangements
A chemical bond
transfer or sharing of electrons that results in a full valence shell
Ionic bonds: electrons are transferred Covalent bonds: electrons are shared Metallic bonds: electrons move around
Ionic Bonds
Electrons Transferred
When one atom loses or gains valence electron, ions are formed 1. Electrons are lost: becomes +ve ion 2. Electrons are gained: becomes – ve ion
Ionic bond form when ions with opposite charges attracted, & Creates ionic compound
Ionic compounds have very different properties than the bonded elements that make them up
Ionic bond, found in Halite (table salt) Na loses a valence electron (becomes +ve) Cl gains a valence electron (becomes – ve) Both have the same charge
Sodium: Soft, silver, toxic metal that reacts explosively when exposed to water
Chlorine: Poisonous green gasA covalent bond forms when electrons are shared between atoms
Metallic Bonds
Electrons Free to Move
form when valence electrons are free to move from one atom to another
All atoms share available valence electrons Movement of e- between atoms results in: 1. High electrical conductivity 2. Malleability 3. Other unique properties of metals
Physical Properties
Minerals have a definite crystalline structure & chemical composition that Gives them unique physical & chemical properties & These properties can be used in identification
Include Luster Ability to transmit light Color Streak Crystal Shape or Habit Strength (Tenacity, Hardness, Cleavage, Fracture) Density & Specific Gravity other distinctive properties (Taste, Feel, Smell, Magnetism, Optical properties, &Effervescence)
Luster
quality of light reflected from the surface of a mineral
Types of Luster metallic: Minerals that look like shiny metal submetallic: appears slightly dull Nonmetallic: Vitreous or glassy, dull, earthy, pearly, silky, & greasy
Ability to transmit light
opaque: do not transmit light are translucent: transmit light, but not image transparent: transmit both light & images
Color
may be one of the most obvious properties of a mineral, but it is only a diagnostic property for a few minerals
Slight variations in the chemical composition can change the color dramatically
Color
Streak
is the color of a mineral in powdered form Obtained by rubbing the sample on an unglazed porcelain tile (streak plate) Streak, unlike color, is generally consistent Metallic minerals have a dense, & dark streak Nonmetallic have a light streak Not all minerals produce a streak
Streak
Crystal shape or habit
is the characteristic shape of individual mineral crystals Most minerals grow in one common shape, but some have 2 or more shapes
Crystal HabitCrystal Habit
strength
determined by the strength of chemical bonds &determines how minerals break or deform under stress
Include Tenacity, Hardness, Cleavage, Fracture
Tenacity
resistance to breaking or deforming
Minerals with ionic bonds tend to be brittle, shatter under stress
Minerals with metallic bonds are malleable, deformed into shapes & thin sheets
Sectile minerals cut into thin shavings
Elastic minerals return to its original shape after being bent
Hardness
resistance to abrasion or scratching measured on a scale of 1 to 10 (Moh’s Scale) Can be determined by rubbing the mineral against a material of known hardness
Cleavage
tendency of a mineral to break along planes of weak bonding This produces smooth, & flat surfaces Not all minerals have cleavage Cleavage easily confused with crystal shape cleavage is visible when a mineral is broken
Fracture
property resulting from chemical bonds that are approximately equal in strength Irregular: uneven broken surface Conchoidal: smooth, curved broken surface Some minerals exhibit splintery or fibrous broken surfaces
Fracture
Density & Specific Gravity
Specific gravity describes the density Specific gravity G: Ratio of a mineral’s weight to an equal volume of water Most minerals have G between 2 & 3 Many of the metallic minerals have a much higher G (20 for gold) G estimated by hefting mineral in your hand
other distinctive properties
Taste halite is salty Feel talc is soapy, & graphite is greasy Smell sulfur smells like rotten eggs Magnetism some can be picked up by a magnet & some can pick up iron objects Optical properties calcite refracts light Effervescence carbonate minerals fizz when exposed to dilute acid HCl
Double refraction in calcite Optical properties, & Interaction with HCl for carbonaceous minerals EffervescenceSummary
Mineral Groups
There are > 4000 named minerals, but only a few are abundant in Earth’s crust known as rock-forming minerals
Economic minerals are less common than rock-forming minerals, but are used in the manufacture of products
silicate groups: Silica & oxygen combined to form the basic building block for the silicates The most common minerals More than 800 silicate minerals Make up 90% of the Earth’s crust
The remaining mineral groups referred to as the nonsilicates Far less abundant in Earth’s crust Some are very important economic minerals
The majority of rock-forming minerals are made up of only eight elementsThe silicon-oxygen tetrahedron is the building block of all silicates Four O surround Si atom Tetrahedra can be joined into chains, sheets, or 3D networks by sharing O atoms
Silicate Minerals
Feldspars are the most common silicates, > 50% of Earth’s crust
Quartz is second-most abundant mineral in continental crust
Only common mineral composed completely of Si & O
Silicate minerals tend to cleave between the strong silicon-oxygen structures
Most silicate minerals crystallize from molten rock as it cools
Environment & chemical composition determines which minerals are produced
Some silicate minerals form at Earth’s surface as other silicates are weathered
Some silicate minerals form at extreme pressures during mountain building
Common light silicate minerals Feldspar, Quartz, Muscovite, Clay mineral (Contain Al, K, Ca, & Na)
Dark silicate minerals iron, magnesium, Pyroxenes, Amphiboles, Olivine, Biotite, Garnet
Dark color & high G from iron contentFeldspars the most abundant In Igneous, Sedimentary & Metamorphic Have 2 directions of cleavage at 90º hardness = 6 K-feldspar contains K ions Plagioclase feldspar contains Ca & Na ions, & has striated cleavage surfacesQuartz In Igneous, Sedimentary, & Metamorphic Impurities cause a variety of colors hardness = 7 Crystal Forms hexagonal + pyramidMuscovite member of the mica family Excellent cleavage in one direction hardness = 2.5Clay minerals the weathering product of other silicates Common part of soil Nearly half of the volume of sedimentary rocks is clay mineralsOlivine major constituent of dark igneous rocks Abundant in Earth’s upper mantle Black to olive green, glassy luster, granularPyroxenes important in dark-colored igneous rocks Augite is black, opaque, & has 2 directions of cleavage at nearly 90º
Amphibole group includes minerals that commonly make up dark portion of light-colored rocks Hornblende is a dark black mineral with two cleavage planes at 60º and 120ºBiotite is a dark, iron-rich member of the mica Excellent cleavage in one direction Common in light-colored rocksGarnet is a dark silicate Glassy luster, no cleavage, conchoidal Color varies, but commonly deep redNonsilicate minerals divided into groups based on the – ve charged ion common to the group Nonsilicates make up only about 8% of crust Found in significant amount in sedimentary Some are economically important
Carbonates contain a carbonate ion CO₃²- Calcite & dolomite Used: in road, building stone, & cement
halide Halite is table salt
sulfate Gypsum is used in plaster
Halite & gypsum are common evaporites
Oxides are important iron ores
Other economically important Sulfides (galena, sphalerite) Native elements (gold, silver, copper) Fluorite Corundum (ruby, sapphire) Uraninite
Summary
Minerals divided into rock forming menirals that form solid earth & Valuable (economic value), Both may be Silicates or Non-silicates
Silicates (the most common) are based on the silicon-oxygen tetrahedron, Subdivided into light & dark groups
Nonsilicates include -ve ion, common in sedimentary rocks, & Many ot them are economically important
System: group of interacting, or interdependent parts, form a complex whole
Types of systems: 1. Closed system نظام مغلق 2. Open system نظام مفتوح 3. Isolated system نظام معزول
Earth is a system composed of numerous interacting parts called subsystems
The hydrosphere ,atmosphere, biosphere, & solid earth are subsystems in the whole earth system
Earth is characterized by continuous Interactions between these spheresShoreline: meeting place for rock,water,&airSolid earth, or geosphereGeosphereAtmosphereHydrosphereResources & environmental issues Most of Earth science may characterized as environmental science
The Nature of Scientific Inquiry
Natural world behaves in a consistent & predictable manner
SCIENTIFIC METHODS 1.Collecting data (facts) through observation & measurement 2.Constructing one or more than one preliminary, untested explanation, called scientific hypothesis 3.This hypothesis must pass objective testing & analysis 4. When hypothesis has been tested & widely accepted by scientists it elevated to a theory
Data→hypothesis→testing, analysis→theory
Paradigms
Theories that are : extensively documented Held with a very high degree of confidence Comprehensive Explain a large number of interrelated aspects of the natural world Ex. Theory of plate tectonics
Each Mineral composed of element in various combination
elements composed fundamental building block of matter: Proton, Neutron, & Electron
Mass of p⁺ = Mass of neutron > Mass of e-
P⁺ & n held together in nucleus by attractive force
Atomic number (Z): Each element has specific number of p⁺ in nucleus & Z is number of Proton
Number of n = Number of p⁺ for elements with small Atomic number, & Number of n > Number of p⁺ for elements with higher Atomic number تتساوى اعداد النيوترونات مع البروتونات بالعناصر الخفيفة وتزداد بالعناصر الثقيلة: لان كلما زاد عدد البروتونات تزداد قوى التنافر بينها (عدم استقرار النواة) فيزداد عدد النيوترونات لتصل الذرة للاستقرار وكلما زاد عدد النيوترونات يزداد العدد الكتلي وتنتج العناصر الثقيلة “قابلة للانشطار”
Isotope: element has different number of n
mass number : sum of number of n & p⁺
atomic mass : mass of atom divided by one-twelfth mass of ¹²C atom
Except for ¹²C atomic mass is just trifle different from mass number, Because each isotope has different number of n so each isotope must have different atomic mass
atomic weight: average weight of atomic masses of isotopes, depends on isotopic composition
Only 83 elements are available to make minerals: from 112 element in periodic table only 94 occur naturally, 11 of 94 are geologically ephemeral (occur in small amounts as short-lived radioactive isotopes produced by n-capture or radioactive decay & so it decay rapidly) عناصر لا تدخل بتركيب المعادن (الغازات النبيلة العناصر النشطة والمصنعة بالمختبرات) والعناصر النشطة لا تدخل لان فترة وجودها صغيرة فهي تتحول لعناصر اخرى ضمن سلسلة من التفاعلات
ELECTRONS
In uncharged atom: number of e- = number of p⁺
Electron don’t orbit randomly around nucleus, but systematically organized into energy level with 4 quantum number
Pauli Exclusion Principle: no 2e- can have same of 4 quantum number
Principal Number (η) يصف مستويات الطاقة والبعد عن النواة have any +ve integer value
energy of e- depend on η higher η → higher energy Because higher energy associated with greater distance from nucleus
η are correlated with shells that traditionally are identified with letters (K, L, M, N…etc) Angular Momentum Number (l) Depend on value of η : L = [0, (n – 1)] distinguishes subshells with different shapes يصف شكل المدار
Calculation maximum subshell number within shell is limited to n – 1 For K shell: l = η – 1 = 0 →(l=0) has 1s For L shell: l = 2 – 1 = 1 → (l=1) 2s & 2p
subshell identified with η of shell & letter of subshell Ex. p subshell in (n=2) is 2p
magnetic quantum number (Mι) Depend on value of l : Mι = [-l,+l] number of orbitals within subshell = 2l + l It distinguishes among different orbitals with different orientations within subshell يصف اتجاه المدارات
Spin quantum number (Ms) Each orbital contain 2e- distinguished by Ms, & the Values of Ms = +½ or ½ electron behave spinning (magnet) on axis, so Ms taken to indicate spin to right & left each spinning charged e- behave like simple magnet with north & south pole Because magnetic field generated by movement of e- If electron spins are balanced, so number of right & left spins is same & no net magnetic moment formed if e- spin aren’t balanced, net magnetic moment result
range of energy levels in subshell of different shell overlap : progression of increase energy level is shown in Figure : 1s < 2s < 2p < 3s < 3p < 4s < 3d….
valence electrons
elements at right side of table (noble gasses) have all of their subshells filled
Core: inner shell configuration, within shells are entirely filled
Valence electrons: outer shell configuration within shells that are not entirely filled
If core is identical to electron configuration of noble gas It’s called noble-gas core Ex, Na has Ne noble-gas core + single 3s valence electron
A pseudonoble-gas core consists of noble gas core + entirely filled d & f subshell Ex. Arsenic (As) has pseudonoble gas core 1s, 2s,2p,3s,3p,4s, & 3d subshells + three 4p valence electrons
Formation Of Ions
Ions: atoms with excess or deficiency of e- compared to number of p⁺ in nucleus
Anions: Ion with net -ve charge because have more e- than p⁺
Cations: Ion with net +Ve charge because have fewer e- than p⁺
valence or oxidation state: charge of ion
Whether element will form anion or cation can be inferred from configuration of valence electrons
Cation Vs. Anion
Metals that have noble gas or pseudonoble gas cores, have Little energy to lose valence e- to form electron configuration of noble gas, so they form cation
Nonmetals, have valence subshells that need few e- to be filled, & nonmetals have strong affinity for e- to fill outer subshell to form anion
Electronegativity (δ-) measure propensity of element to gain or lose electrons
Elements with low δ- lose outer valence e- readily to form cations Elements with high δ- have strong affinity for extra e- & tend to form anion
δ- values are used to estimate nature of chemical bondsعدد التأكسد الممكن لجميع العناصر
ABUNDANCE OF THE ELEMENTS
8 element are present in substantial amounts (O, Si, Al, Fe, Ca, Na, K, & Mg) comprise large majority of crust, & are elements from which most common minerals are composed (all are cation except O)
The oceanic crust is richer in Fe & Mg (Basalt) than average crust
Determining composition of entire Earth is even more difficult because mantle & core cannot be sampled directly, & Estimates are obtained by: 1. Earth’s mass & density distribution as determined by geophysics 2. Composition of basalt derived from mantle & samples of mantle that arrive with magma 3. Composition of meteorites, represent material from which Earth accreted 4. Applying appropriate cosmological, geochemical, & petrophysical models to evaluate these data
Some mineral have different bond types, such as Graphite: 1. Covalent σ & π bonds 2. Intermediate covalent/metallic character 3. Van Der Waals bonds
bonds involve valence electrons (Valence Related Bonding)
involve mechanisms allow elements to acquire of noble gas or pseudo-noble- gas configuration by gain, loss, or sharing valence electron, would be in lower-energy, & form stable configuration
Types of Valence Related Bonding 1. ionic bond 2. covalent bond (sigma σ or Pi π) 3. metallic bond (conduction, valence)band
Bond Not Involving Valence Electron
depend on relatively weak electrostatic forces that can develop because of asymmetric charge distribution
These bonds are sometimes referred to as molecular or intermolecular bonds
2 mechanisms by which asymmetric charge distribution is developed are illustrated by hydrogen & Van Der Waals bonding
Types of bonds don’t involve valence e- 1. van der Waals 2. hydrogen bonding
Ionic Bond
formed by electrostatic attraction between +ve & – ve ions (Anion + Cation)
Ex. halite (NaCI) make ionic bound because: 1. Exchange of electron between Na (loss) & Cl (gains) produce stable electron configuration for both 2. Na (+ve) & Cl (-ve) have opposite charges
Nature of attractive force between oppositely charged given by Coulomb law F α (q₁* q₂) / d²
Equilibrium distance between Na & Cl is given where F = 0 (At greater distances attractive force & smaller distances repulsive force is larger) F=0 → Fattractive = Frepulsive
Charges must balance Ion bonds together if net +ve charge = net -ve charge
Ionic bond fairly strong because: 1. Ion act like charged sphere & pack together in systematic & symmetrical manner 2. +ve & -ve charges alternate to form electrical neutral crystalline solid, This represent low-energy configuration
Ionic-bonded crystals tend to be brittle
Ionic crystals have strong resistance to sliding different parts past each other Because like charges repel each other
Forcing issue result in rupture rather than ductile deformation Because structures quite orderly
Failure commonly occur along cleavage plane
Covalent Bond
formed by sharing of electrons, & occurs when orbitals of 2 atoms overlap
Provided overlapping orbitals have no more than 2 electrons combined
electrons in orbital begin move about both atom because attracted to nuclei of both atom, bond established
Strength of covalent bonds is function of degree to which orbitals of adjacent atoms overlap, & more overlap yields stronger bonds (such as in diamond)
Ionic bond not possible in diamond because: 1. all C have identical electron configuration & affinity for valence electron 2. One C cannot steal electron from another to form +ve & – ve ions
Types of covalent bond: 1. sigma (σ): has high degree of symmetry about axis parallel to length of orbitals that overlap end to end, like bond in diamond 2. pi bonds (π): orbitals overlap side to side, so e- shared laterally, found in graphite
In diamond, high degree of overlap produces very strong bond Diamond composed of (C) & noble-gas configuration obtained by gaining or losing 4e-, & To produce covalent bond it must be share 4e-, but in ground-state configuration of C only three 2p orbitals are available, 2 have e- & third has none, & 2s orbitals cannot share nay e- because contains 2e- & To create 4 unpaired orbitals, hybrid orbitals formed: 1. One of e- in 2s promoted to vacant 2p orbital; this provides 4 unpaired orbitals 2. Because all 4 bond to adjacent C must be identical, orbital in 2s & 2p hybridized into 4 identical 3sp³ orbital 3. Each of orbitals consists large lobe pointing in one direction & small in opposite, positioned around nucleus so that large lobes define corners on tetrahedron 4. Each of 3sp shared with identical hybrid orbital to form continuous crystal structure of diamond, Each are sigma σ covalent bondsBond in graphite π & σ bonding within sheets of C is very strong, stronger than bonds in diamond, That attested by observation that C-C bonds in graphite are shorter than in diamond
low hardness of graphite is consequence of van der Waals bonds that hold sheets together
Metallic Bonds
considered to type of covalent bond in which valence electrons delocalized & free to move throughout crystal structure
Formation of metallic bonds depends on: 1. Valence electrons held weakly: like Metals that have low electronigativity 2. Number of electron shared must be large 3. Availability of vacant energy levels into which valence electrons can readily move: This is controlled by spacing between atoms
If spacing between atoms = infinite, so all atoms have same energy level & orbitals
Width of energy band produced by subshell increases as a proximity of atoms increases
e- become free to migrate throughout structure if: 1. energy level of unfilled band overlaps that of filled band 2. outer valence subshell is only partially filled
Mg illustrates overlap of unfilled band with filled band, When Mg atoms placed in close proximity, width of energy band increase so 3s & 3p band overlap
Abundance of available energy levels allows electrons to migrate easily via structure
conduction bandband has more energy level than their electrons & can conduct electrons via crystal if voltage is applied, such ad 3p band in Mg
valence bandprovide electrons move into conduction band, such as 3s band in Mg
inner subshells don’t contribute to electrical conduction because energy gap, known as band gap, is present between bands
Na have conduction band + valence band
Only half of energy levels in 3s band can be occupied at any one time so remaining energy levels are available for conduction
Transition metal utilize both mechanisms to produce metallic bond, conduction occur in d band (contain unfilled orbitals) & energy level of d band overlap higher s & p bands
Metalic bond no directional because metalic bond don’t involve matching specific orbital on adjacent atoms,
Metals atoms back together in highly symmetrical manner & held together by weak bonds provided by valence e- migrating throughout structure in conductiin band
Because metalic bonds are weak metals tend to be relatively soft & malleable
Because metal atoms have their valence requirements satisfied by sea of valence e-, it very easy for one metal atom to substitute for another in crystal structure
Width of energy bands increases as atoms are brought closer together
Hydrogen Bonding
Ice is most familiar mineral have H-bond
Ice composed of H₂O, Bonding occurs because H₂O polar molecule, 2H covalently bond to O by sharing electrons
Polar: Because O has high electronigativity than H, it places greater claim on shared electrons than do H & This produces electrical polarity to water molecule
Water molecule
Van Der Waals Bonds
Depend on asymmetrical charge distribution, but asymmetry is produced in different way
Van der Waals bonds are quite weak, & mineral have them (graphite & talc) are soft & greasy
soft & greasy properties used to advantage: 1. graphite soft & black, used to make pencil, with which sheets slide past each other 2. Talc used as body powder because it is soft & helps prevent chafing of tender skin 3. Weakness found in clay minerals also leads to major engineering problem, known as swelling soil
In Graphite that consist sheet of C covalently σ & π bonded more -ve charged electron on one side than other producing polarization, & polarization on one sheet are similar in its neighborse, & Van Der Waals pond produced by weak electrostatic atraction between opposite charge of poth sheets
Relation among Valence-Dependent Bond
values of electronegativity can be used to estimate the nature of chemical bond 1. Ionic bonding should be expected if δ- is quite different 2. Covalent & Metallic involve sharing of e- among atoms with similar affinity for e- & small or zero difference in δ-
Crystals with ionic & covalent bond have low electrical conductivity because: 1. Valenc e- held tightly in specific orbital 2. Electrical conductivity increases if crystals heated because thermal energy increases
Crystals with metallic bonds have high electrical conductivity because: 1. Electron are free to migrate throughout structure in conduction bands 2. Electrical conductivity of metallic bonds decreases as temperature increases because greater thermal vibrational energy of lattice tends to impede migration of electron
mathematical relationship is Percent ionic character
Figure show: Empirical relationship between difference in δ- & degree of ionic character producedNative elements, like diamond C, graphite C, sulfur S, gold Au, & silver Ag, form bonds in Δδ- = zero, These bond are intermediate between covalent & metallic
Sulfate → covalent + metallic
Silicate → covalent + ionic
Cation Vs Anion
About atoms!
Volume occupied by proton, neutron, & electron that comprise isolated atom or ion defined by probability of finding electrons at specific locations around nucleus
Probability aren’t spherical, except electron in s shells, & don’t have defined boundaries
Some probability, always exists of finding electron at great distance from nucleus
Chemical bond involve some degree of covalent bonding in which orbital from atoms or ions are inferred to overlap, to allow sharing electrons
Effective radius
Atom behave as little sphere, It convenient to define sizes of atoms in term of effective radius based on distance between centers of atoms
Effective radius of atom or ion: is size it would have if it behaved like small hard sphere
Atomic radius: effective radius of uncharged atom
Ionic radius: effective radius of anion or cation
In covalent or metallic bond bond length (L) is equal to 2 effective radius 2R L = 2R
– Techniques of X-ray diffraction used to measure bond length & sum of effective radius of atoms
– There are 2 sets of data depending on nature of chemical bonds involved: 1. For metals & semimetals, radii based on metallic bonding in structures in which atoms closely packed so that each atom is in contact with 12 other atoms 2. For non-metals, radii based on single covalent bonds
In ionic-bond, length between anion & cation = to sum of effective ionic radii of cation Rc & anion Ra L = Rc + Ra
Techniques of X-ray measurement length between anions & cations but cannot tell us how much of bond length to allot to cation & how much to anion
to estimate of effective ionic radii of anions & cations: 1. Comparing different structure 2. Evaluate cation-anion & anion-anion distance
principal variables influence effective ionic radius: 1. Oxidation state (valence) of ion 2. Coordination Number (CN): Number of anions in contact with cation 3. spin state: factor in transition metals with d orbitals
Oxidation State & Coordination Number
Cations are smaller than uncharged atom Increase +ve charge produce smaller ion (size decreases) because electron held more tightly& closely to nucleus
Anions are larger than uncharged atom because nucleus is less able to hold additional electrons tightly
Interatomic distances, & effective ionic radii, influenced by number of anions contact with cation (CN)
Anions larger than cations, so structure considered to consist framework of packed anions with smaller cation tucked into interstice, or hole between anions
size of interstice determine by coordination number (CN)
large hole require more anion to define boundaries
coordination number of 4 -for example- involves 4 anion arranged at corners of tetrahedron with small space in middle in which small cation may reside
as coordination number increases, effective ionic radius of cations occupying hole defined by anions
cations expand or shrink to fill space available between anions
High spin state ions have minimum pairing of electrons in d orbitals; & low have maximum pairing & smaller
high spin state is preferred because having unpaired electrons represents lower energy configuration than having paired electrons within d orbital
some bonding geometries require hybridization that favors low-spin configuration
Iron exhibits different spin states Under crustal conditions, high-spin configuration dominates in most minerals
Copyright: INTRODUCTION TO MINERALOGY, WIILIAM D. NESSE, 2nd Edition
Crystallography
Crystallography
Crystallography: describe shape, symmetry, & crystal structure of minerals
Tools used to described Crystals: 1. X-ray 2. petrographic microscopes 3. scanning electron microscopes
Symmetry “in general”
Types of Symmetry 1. Translational Symmetry (in 2D & 3D) 2. pointSymmetry 3. space groups
The most important concepts: 1. Translational: unit cell, unit mesh, plane lattice, space lattice, crystal axes, crystal systems, Bravais lattice 2. point: reflection, rotation, inversion, 32 point groups or crystal class 3. space groups: combine translational symmetry with point symmetry operations to produce glide & screw symmetry
Nomenclature of Crystals
Crystal faces: have rational orientations relative to crystal lattices
Miller indices: described & identified individual crystal face or crystallographic plane (Ex. cleavage)
crystallographic directions & zones
crystal forms: described collection of faces of crystal, groups of face, flat, & characteristic shape
crystal habit: general characteristic external shape of crystals
Dimensions a : thickness b : width c : height or length
Angle α : the angle between c & b axis β : the angle between c & a axis γ : the angle between b & a axis
+a = front, -a = back +b = right, -b = left +c = up, -c = down,
2D Translational Symmetry
Important concepts
node: center of each spot at intersection of lattice line
unit meshes: fundamentally different shapes produced by translation nodes parallel to a & b – there are 4 unit meshes: Square, Rectangle, Rhombus, & Parallelogram
plane lattice: continuous repeating pattern of dots produced by translation parallel to a & b – there are 5 plane lattices can be produced by translation in 2D: Square, Rectangle, Diamond, Hexagonal, & Oblique plane lattices
“الفكرة” اي نقطة في الشكل نسميها (نود) وهذه النود تتحرك في بعدين وهم محورين أ و ب وحركتها هذه تصنع اشكال افهم الفكرة لتستمر بفهم القادم very easyحركة النود تصنع 5 plane lattice with 4 unit meshes لان هناك شكلين سيشتركون بوحدة واحدة
شرح الشكل الاول: انتقال النقطة بمسافة متساوية بين محورين أ و ب بزاوية ٩٠° سيصنع مربع 🙂 “وهكذا باقي الاشكال” ما يعني بالشكل الاول a = b, γ = 90° سؤال ذكي 🙂 : اين المحور الثالث؟؟ نحن الى هذه اللحظة نعمل في بعدين ما يعني محورين فقط وزاوية واحدة بينهما ودخول محور ثالث ستزيد عدد الزواية الى 3 وعدد المحاور 3 وهو الانتقال في 3 ابعاد “الموضوع القادم”
المطلوب: فهم كل شكل من الاشكال الخمسة كيف تم اشتقاقهم بمعرفة طول كل من الضلعين والزاوية بينهما واسم الشكل واسم وحدته وهو ملخص بالصورة بالاعلى very easy ❤
ملاحظة: الزواية التي تحتوي على جيب الزاوية او متممتها غير مطلوب اشتقاقها ملاحظة: ممكن يجي جدول بالامتحان فارغ ويُطلب منك تعبئته بالزاوية والابعاد والاسماء واسماء الوحدات
node
node occur at corner, but diamond has centered (C) unit mesh شرح: النقاط دائما تكون على الاطراف الا في centared rectangle (diamond) وهذا ما يفسر ارتباط شكلين في وحدة واحدة وهم diamond & premative rectangle (rectangle) وهذا بسبب طريقة اشتقاقهما، ونلاحظ من الشكل بالاعلى انه لهما نفس الابعاد والزاوية
Unit mesh axes : parallel to edges of unit mesh labeled a & b if they have same length “θ = y”, such as in reactangle & diamond
Ceramic Example a. Square ceramic tile laid in square lattice
b. Rectangular bricks laid in rectangular lattice
c. Rectangular brick laid in diamond lattice, unit mesh includes pieces make 2 bricks
d. Hexagonal ceramic tile laid in hexagonal lattice, rhombic unit mesh includes pieces make one tile
Summary of dimensions & angles
Square: a = b, γ = 90°, Square unit mesh
Rectangle (or P-Rectangle): a ≠ b, γ = 90°, Premative (P) Rectangle unit mesh
Diamond (or C-Rectangle): a ≠ b’, γ = 90°, Centred (C) Rectangle unit mesh
Hexagonal : a = b, γ =120°, Rhombus
Oblique: a ≠ b’, γ)≠ 90°, Parallelogram
2D Translational Symmetry
Important concepts
Space lattice: 2D plane lattices systematically repeated one above other to allow for translation vector in 3D, & lattice nodes are repeated in all 3 direction
unit cell: volume outlined by lattice nodes
شرح Space lattice ما يعني ان هو انتقال النود (ال5 اشكال) في بعد ثالث تخيل مربع انمط للاعلى مثلا رح ينتج مكعب، وهكذا (يعني بنمد المساحة لانتاج الحجم)
الوحدات plane lattice → unit mesh space lattice → unit cell
edges of unit cells identified (a,b, & c) which intersect at point called origin
Bravais Lattices: 14 different space lattices produced from repeated 5 plane lattices in 3D, & divided into 6 crystal system based on shape of unit cell (triclinic, monoclinic, orthorhombic, hexagonal, tetragonal, & isometric)
Primitive (P): unit cells contain lattice nodes only at the corners
Body-centered (I): unit cells contain an additional lattice node at the center
Face-centered (C): unit cells contain lattice nodes on the corners & on 2 opposite sides
Face-centered (F): unit cells contain lattice nodes at the corners & at the center of each face
Except for triclinic, each crystal system has more than one Bravais lattice (Important for exam)
عند انتقال Oblique plane lattice مسافة للاعلى ليس بزاوية ٩٠° مع كل من المحورين الاصليين ينتج Primitive Triclinic وهذه المجموعة لا يمكن ان تحتوي نود بالوسط لذا دائما Primitive Triclinic الابعاد والزواية والشكل وطريقة تكونه بخانة “ملاحظة” مهم
والاشكال القادمة نفس الشيء هو مجرد انتقال للاشكال التي صنعناها بالبعدين في بعد ثالث
Copyright: Shaas 🙂
Notes
different between face-centered in how crystal axes labeled, in orthorhombic isn’t done consistently
Motif: may be crystal face or particular arrangement of atoms mack up crystal structure
possible point symmetry operations are: 1. reflection (m) 2. rotation (A) 3. inversion (i) – rotoinversion: Rotation combined with inversion to produce symmetry called (1, 2, 3, 4, or 6)-fold rotoinversion axes
Point about which symmetry are recognized center of crystal or origin of unit cell
Reflection (m) produced by mirror plane (m) that passes through crystal structure so the pattern on one side is mirror image of pattern on the other
Only planes in specific orientations can be mirror planes
Monoclinic →1m Triclinic → no mirrors Isometric → 9 m or lessRotational (A) symmetry involves repeating a motif by set of uniform rotations about an axis A₂ →every 180° A₃ →every 120° A₄ →every 90° A₆ → every 60° Inversion (i) center of symmetry, point (corner) have equivalent point in opposite side في الشكل: الشكل الاول يوجد به انعكاس اما الثاني لاCompound Symmetry Operation (Rotoinversion)
À₁: Simplest, produced by (A₂) 360° + i, & can be duplicated
À₂ produced by (2A₂) 180° + i + m, & can be duplicated
À₃ produced by (A₃) 120° + i, & can be duplicated
À₄ cannot be duplicated, 90° rotation followed by i
À₆ produces same result as A₃ at right angles to mirror (A₃ at 60° + m)
شرح: مثلا اذا عملت تدوير لشكل بمقدار 360° ولم يتكرر الوجه ثم كان ممكن تعمل انعكاس يكون يحتوي 1-fold rotoinversion or À₁ وهكذا…
Symmetry Notation
symmetry symbols refer to symmetry operations
هناك طريقتين للتعبير عن الرموز بالشكل ٣ محاور دورانية ثنائية وانعكاس و٣ مُري ونستطيع التعبير عنه كالاتي 1. 3A₂, 3m, i 2. Herman-Mauguin: 2/m,2/m,2/m / = Perpendicular 2 = A₂ Frequency of 2/m = number of A₂
اهملنا الانعكاس لانه يوجد دوران ويوجد مرآة وبالتالي ضمنيا يوجد انعكاس ملاحظات مهمة بما يخص Rotoinversion À₁ = i لانه فعليا التدوير 360° هو العودة لنفس النقطة وبالتالي هو انعكاس عادي لذا يمكننا الاستعاضة عن هذا الرمز واستبداله برمز الانعكاس مباشرة À₂ = m يمكن استبدال هذا الرمز برمز المراي لانه فعليا مجرد انعكاس À₃ = A₃ + i À₆ = A₃ + m
To Determining Crystal System & Crystal Class
Determine center of symmetry Identify any mirror planes then Identify rotation axes & rotoinversion
Symmetry elements of i, A, & m combined in variety of ways, but combinations are limited because symmetry elements must be compatible with each other
In 2D possible symmetry elements are m & A, that may be taken individually or combined to produce l0 different 2D point groupIn 3D symmetry elements are i, m, A, so number of different combination of symmetry increases to 32 (32 point group or crystal class)
Point groups grouped into 6 crystal systems based on common symmetry elements
6 crystal system defined based on unit cell geometry that generated from Bravais lattice
Table shows symmetry elements possessed by crystal classes & crystal system الجدول مهم
Notes
point group for each crystal system can be use any Bravais lattice from that crystal system, but Single exception occurs in hexagonal system where only trigonal division use Rrhombohedral Bravais lattice
اكثرهم تماثل Isometric the most common system in the nature is monoclinic then orthorhombic The least common system in nature is hexagonal then tetragonal
Calcite → Trigonal (Not rare)
hexagonal & trigonal (crystal family)
Space Group
produced by point group + space lattice
There are 230 space groups represent all combinations of point symmetry with translational symmetry
point group symmetry must be consistent with symmetry of lattice, for Ex. Isometric point groups used only with isometric lattices, tetragonal with tetragonal lattices… atc
These combinations yield 73 space groups, so there are 2 additional symmetry operations called glides & screws are possible in 3D, Each is compound symmetry operation
Glide: translation + reflection across mirror (glide) plane Ex. Chain silicate (in pyroxene)
Screw: produced by translation + rotation
Crystal Faces
Crystal faces always grow in rational orientations relative to the crystal lattice
most common faces are parallel to surfaces of unit cell, that parallel to principal planes via crystal lattice
Result with cubic unit cell is cubic crystal, hexagonal unit cell have hexagonal cross section… atc
Tendency of crystal faces to follow simple, rational orientation through crystal lattice has resulted in recognition of 2 related laws of crystallography: 1. Law of Hauy : Crystal faces make simple rational intercepts on crystal axes 2. Law of Bravais : Common crystal faces parallel to lattice plane that have high lattice-node density
• كلما كانت النود “الكثافة” اكثر تزداد فرصة نمو البلورات
• اكثر الاوجه شيوعا اكبرها مساحة وموازية لوحدة الخلية
• اقل البلورات مساحة هي اقل نمو بلورات واقل كثافة
Figure shows P-monoclinic lattice with several potential crystal faces
Planes A, B, & C principal planes in lattice, have high lattice-node density, parallel to faces of unit cell, & it likely crystal faces
Plane T: fairly density & likely crystal face
Plane Q: low density & not likely crystal face
Miller Indices
Because crystal face have rational orientation relative to crystal lattice, it possible to develop short-hand system to describe orientation of crystal faces & crystallographic planes
Miller index: short-hand system describe orientation of crystal faces & crystallographic plane, consist of series of coprime integer that are inversely proportional to intercepts of crystal face or crystallographic plane with edges of unit cell
Miller index has general form hkl, where h, k, & l = a, b, & c crystal axes Respectively – (hkl) = phase – [hkl] = vector – (001) read zero zero one – (112): read one one two
Negative values indicated with bar over top of number – (IT0) read one bar-one zero or one negative-one zero
Because values in Miller index coprime integers, values like (224) arn’t used because all integers divisible by 2, so = (112)
Consider monoclinic mineral that forms crystal with face t, if extended to intersects all 3 crystal axes (Figure a), This face cuts via lattice (Figure b) so that numbers of unit cells out from crystal center on a & b = 2c, Miller index for face t is inverse of these values, then: (12 12 6) = (1 1 ½) = (1 1 ½)-¹ = (1 1 2) = (hkl) This means: face cuts cell at 1 unit along a & b, & half unit cell along c حاول تفهم الي عملو بكل فيس حلو الموضوع ومش كثير صعبIndices & Crystal Axes in Hexagonal System
Crystal axes & indices in hexagonal require some additional explanation because 2 conventions use (a, b, c), & (a₁, a₂, a₃, & c)
Consider (a, b, c) crystal axes located according to 3-axis convention
Consider (a₁, a₂, a₃, & c) 4 axes, Miller-Bravais index contains 4 integers (hkil)
دائماً يكون h + k + i = 0
للحويل بين النظامين فقط قم بحذف i
Mathematically: Determine Miller Index: require 2 piece of data
1. Axial intercepts for crystal face (i)
2. unit cell dimension or axial ratio (a:b:c)
هي اطوال المحاور تقسم جميع الاطوال على الطول الاوسط (ب) بحال اعطاك السؤال نسبة جاهزة لا تقسم “بدون وحدة” اذا حصلت على النسبة، والتقاطع تستطيع الحساب بقسمة النسبة على التقاطع او العكس “مع اخذ المقلوب” Calculating the Miller index of x face if the unit cell dimensions are a = 9.73 A°, b = 8.91A°, & c = 5.25 A° اولا نحسب النسبة “القانون الاول” a : b : c = 9.73/8.91 : 8.91/8.91 : 5.25/8.91 a : b : c = 1.09 : 1 : 0.59 ثانيا نقسم النسبة على التقاطع “القانون الثاني” (hkl) α (1.09/3.82) (1/3.5) (0.59/2.07) (hkl) α (0.28 0.28 0.29) So. (hkl) α (1 1 1)
Zones
Zone
collection of crystal faces all of which are parallel to common line called zone axis
Zone identified with index of zone axis [uvw]
For example, tetragonal prism constitutes zone because faces parallel to common line (c axis) through middle of prism, zone axis is there fore 001
zone axis also is parallel to edges defined by intersection of the faces
Crystal Forms
crystal forms
collection of equivalent crystal faces that are related to each other by symmetry of the mineral
A form may be either: 1. open form O: doesn’t entirely enclose volume 2. closed form C: entirely encloses volume
Each crystal form identified by braces { } around hkl Miller index of one of the faces that comprise the form
{011} identifies 4 faces equivalent to (011) {100} identifies 2 faces equivalent to (100) Isometric Forms 15 different forms, all of them are closed, is possible in the isometric system
most common are – cube {001} – octahedron{111} – tetrahedron{111} – rhombic dodecahedron{110}
Nonisometric Forms (disphenoid)
The no isometric forms are also known as disphenoid
possible in tetragonal, hexagonal, orthorhombic, monoclinic, & triclinic
consist of : 1. PEDION or MONOHEDRON (O): single face with no geometrically equivalent face elsewhere on crystal, No symmetry element repeats the face
2. PINACOID or PARALLELHEDRON (O): 2 parallel faces on opposite sides related by i or m
3. DIHEDRON (O): 2 nonparallel faces A. DOME related by m B. SPHENOID related by A₂
4. PRISM (O): 3,4,6,8, or 12 face intersect in set of mutually parallel edge forming tube named based on shape of cross section & Faces that close ends of prism aren’t part of form
5. PYRAMID (O): 3, 4, 6, 8, or 12 non-parallel face intersect at point, named based on cross section, may be either top or bottom
6. DIPYRAMID (C): 2 pyramid related by reflection, with 6, 8, 12, 16, or 24 faces
7. TRAPEZOHEDRON (C): 6, 8, or 12 trapezoid faces, faces on one end offset relative to faces on other, for Ex. Tetragonal trapezohedron have 8 faces, 4 on top & 4 on bottom
8. SCALENOHEDRONS (C): 8 or 12 scalene triangle faces, faces appear to be arranged in pairs
9. RHOMBOHEDRONS (C): 6 rhomb faces, looks like cube that stretched from corner to corner
10. TETRAHEDRONS (C): 4 triangular faces: A. ln tetragonal system (tetragonal tetrahedron): 4 faces are identical isosceles triangles B. ln orthorhombic system (rhombic tetrahedron): face form 2 pair different isosceles triangle
Combining Crystal Forms
Simple crystals may consist of only single closed form such as cube or dipyramid; more complex crystals may include several different open and/or closed forms
All forms on any given crystal must be compatible with one another: mineral crystallizes in isometric system include isometric forms…atc
mineral can have only forms that consistent with symmetry of crystal class to which it belongs Ex. pinacoid isn’t composed of 2 pedion but 2 parallel face related by symmetry cube consists of six equivalent faces; it is not composed of three pinacoid
Forms that occur in 32 point group (crystal class) within 6 crystal systems limited by symmetry of point group Ex. tetragonal prism have single A4 they found only in tetragonal point groups that have single A4
CRYSTAL HABIT
Minerals may or may not display crystal faces depending on conditions of growth
A. Euhedral: display well-formed faces B. Subhedral: crystal faces are present, but are not well-formed C. Anhedral: without crystal facesمهم range of terminology used to describe relative dimensions of individual crystals or grainsPatterns of mineral growth a. Elongate: form parallel, radiating, or felted masses b. Platy or micaceous: form foliated or plumose arrangements c. Equant: form fine-to coarse-grained granular masses
Copyright: INTRODUCTION TO MINERALOGY, WIILIAM D. NESSE, 2nd Edition
Introduction
The term minerals
is used in a variety of ways:
In economic: any valuable material extracted from the earth like coal, oil, sand, gravel, iron ore, & groundwater
In nutritionists: any of the chemical compounds or elements that are important for health
common usage: anything that is neither animal nor vegetable
In geoligy: naturally occurring with crystalline solid
Some definition require inorganic material, but some mineral have organic material called bio mineral
Mineralogy: study of minerals
naturally occurring
formed without benefit of human action in natural environment
synthetic mineral: crystalline solid produce in laboratory (It’s not mineral Because it’s not naturally occurring)
crystalline
atom comprise crystalline material arranged & bonded in regular & repeating long-rang pattern
amorphous: Solid like glass & opal lacking long-range order
Mineraloids: mineral-like, materials that lack long-range crystalline structure, include amorphous solid such as Opal & Glasses
Opal SiO₂.H₂O: consist silica gel arrange in small spherical masses
Any crystalline structure is solid material, but not every solid material have crystalline structure
Metamict: applied to disrupted structures, & once structure becomes metamict then it’s mineraloid
Composition & Properties
As consequence of being crystalline solid, minerals have definite & not necessarily fixed chemical composition – Ex. Quartz SiO₂
composition of many mineral species may vary within limits – Ex. olivine: may rich in iron Fe₂SiO₄ or magnesium Mg₂SiO₄, or intermediate composition
different sample of mineral may have different compositions but variability is limited, Because minerals are crystalline & have definite chemical composition & definite physical properties – في الوحدات القادمة سنعلم ان السبب هو احلال العناصر
physical properties may vary within limits because they controlled by variation in chemical properties
bio mineral “in general”
bio minerals: Minerals constitute integral part of biologic structures & processes
Calcite & Aragonite (both CaCO₃): form shell & major component of limestone layers
Apatite: makes teeth & bones
Bacteria are integral part of geochemical processes at or near surface & influence at many minerals
pyrite FeS₂: found in shale & coal, & reduced by action of sulfate-reducing bacteria
Geomicrobiology: study of interaction of microbes & geologic processes
biologic processes : affect surface chemical environment & therefore types of distribution of minerals found
meteorite impacts
Pseu-dotachylite: Frictional melts produced in fault zones in response to intense shearing
If meteorite impacts are large enough, release high energy to melt rocks that they strike producing impact melt
impact melt ejected from impact crater
Tektite: Small mass of glass, interpreted to samples of now-solidified
lightning strike may heat soil or rock sufficiently to melt some of it & produce fulgurite
Burring coal beds generate heat to fuse surrounding rook (forming scoriaceous or slag-like glasses referred to as ash glass or clinker)
MINERAL NOMENCLATURE
Mineral Species: mineral distinguished from other minerals by combination of composition & structure
Mineral Variety: distinguished by differences in color, habit (shape)… atc
Mineral Series: is 2 or more minerals among there range of composition (Ex. Plagioclase)
Mineral Group: set of minerals with same structure & different compositions
Mineral Crystal: piece of mineral bounded by regular crystal faces produced as crystal grew, Like fracture, & cleavage
Commission on New Minerals Nomenclature & Classification of International Mineralogical Association
holds special interest because of: 1. Appearance & extinction of Dinosaurs 2. Colorful strata that highlight the stunning landscapes of the canyon & plateau country of the southern USA, Ma’in (Triassic) & Kurnub Sandstone (Cretaceous) Formations in Jordan 3. The black shales which is important in many continents. 4. Cretaceous strata are especially important economically because they contain the world’s second largest coal reserves and a large share of its petroleum 5. Global tectonic revolution which cased the breakup of Gondwana, change of climate & nonmarine plants & vertebrates
Opening of the North Atlantic
The breakup of Pangea began near the end of the Triassic Period between present North America & Africa
The breakup was caused by change of convection following a long period of heat accumulation in the mantle, due to the insulating effect of the super continent
The breakup proceeded rapidly during later Mesozoic time with the ultimate separation of Greenland from North America at the end of the Cretaceous Period
During the middle Jurassic, the southern margin of N-America began separating from S-America to form Gulf of Mexico basin
such structures typically form at the triple junction where super continent first breakup
Initial breakup of a supercontinent by:
Heating & doming rifting & sea-floor spreading based upon the N-Atlantic & Gulf of Mexico basin
block faulting, basaltic dikes, volcanic eruptions, & non marine sedimentation
normal marine passive-margin deposition including reefs,tethyan fauna had become established in Gulf of MexicoPaleotectonic map for middle Jurassic time showing the initial opening of the N-Atlantic & Gulf of Mexico ocean basinsPaleotectonic map for end of Cretaceous time showing the opining of N-America Atlantic ocean basin
initial separation of Greenland by opening of the Labrador Seaway & separation of Italy from the Iberian Peninsula
The Caribbean plate carrying Cuba also is shown forming between North & South America
Dark color shows new cretaceous sea floor
Late Triassic to Early Jurassic rifting also disrupted the connection between northern Africa and Europe
Mesozoic Geology
The Sonoman orogeny occurred in Permo- Triassic time
The craton remained above sea level meanwhile, & Triassic non marine red-bed deposition followed that of the late Permian time
Worldwide Cretaceous transgression was the last major flooding of continents – It was caused mainly by rapid sea floor spreading & the resulting enlargment of the ocean ridges, which displaced much sea water onto the continents
Effects of the transgression varied greatly, depending upon topography, climate, & availability of sediments in different regions
The rise of sea level was so great that pelagic sedimentation normally confined to the deep seas spread onto some cratons & produced chalk and black shale deposits
Mesozoic Paleoclimate Global paleoclimate was influenced by feedback effects of the transgression
The climate during late Mesozoic was warm & uniform as it indicated from the following points fossils & oxygen isotope data
The warm climate was caused by the enlargement of sea area coupled with location of both poles in oceanic areas & the excess CO₂ resulted from volcanic eruption
Mesozoic Stratified Rocks in Jordan
Triassic Formations: (from oldest) 1. Main Formation 2. Dardur Formation 3. Ain Musa Formation 4. Hisban Formation 5. Mukeiris Formation 6. Iraq El amir Formation 7. Um Tina Formation 8. Abu Ruweis Formation
Cratonic Disturbances the N-American craton suffered more severe deformation in the late Carboniferous time than ever before
The most intense disturbances occurred in the southern part of the Craton, represented by Colorado & the Oklahoma Mountains
Its believed that these mountains were internal cratonic by-products of the collision of Gondwanaland with southern N-America
Appalachian or Alleghanian Orogeny occurred between late Pennsylvanian & late Triassic times
summarizes the Paleozoic history of the Appalachian belt in plate tectonics terms
Cambrian rifting formed proto-Atlantic Ocean (PA) & Piedmont microcontinent (P)
Ordovician subduction & closing of marginal ocean resulted in collision of microcontinent with N-America by beginning of Silurian (Taconian orogeny)
Subduction of proto-Atlantic plate.
Continued subduction resulted in Permian collision of Gondwanaland (G) with N-America, which in turn caused 5 large-scale overthrust faulting (Appalachian orogeny) Early Mesozoic rifting initiated present Atlantic Ocean (AO)
Late Paleozoic Mountain Building in Eurasia
The end of Paleozoic Era was a time of unusually widespread mountain building, the result largely of several continental collisions.
These produced a gigantic, interconnected supper continent called Pangea.
Hercynian orogenic belt was in Central Europe, which caused by the collision of North Africa with Europe.
Similar-aged deformation around the southern perimeter of the Siberian craton may have resulted from the collisions of several small Chinese cratons
Upheaval of the Ural belt at this time resulted from collision between lithosphere plates carrying Siberia and Europe
Gondwanaland
The name Gondwana is derived from an ancient tribe in India
Gondwana consists of South America, Antarctica, South Africa, Australia & India
In Late Paleozoic time, Gondwanaland collided with N-America & Europe, which caused Permo-Triassic Gondwana Orogeny
Gondwanaland have some similar features based on which geologists can reconstruct Paleo-continent Gondwana, some of these: – Because much land area lay at high latitudes in late Paleozoic time, large ice sheets formed on up-land areas – On the five southern continents, the Gondwana succession has prominent glacial tillites in its lower part. – Gondwana strata containing coal seams & Glossopteris flora. – Gondwana rock succession is capped everywhere either by thick basalt flow rocks or by dikes & sills
Distribution of Gondwana rocks showing their remarkable similarity on all five southern continents Lower Gondwana tillite This is the most famous ancient glacial deposit in the world, formed in in South Africa cratonStriated glaciated surface beneath the Carboniferous Tillite, South AfricaGiant “dropstone” released by a melting iceberg as it floated away from Gondwana ice sheet during Permian
Notice how the layered marine sediments were bent downward by impact & then smoothly buried the dropstone once normal, quiet marine deposition had resumedTongue-shaped leaves of the characteristic Gondwana seed ferns Glossopteris (name means ‘tongue fern”) Found on all the southern continents (including India, Madagascar, & Antarctica) during the Permian, Its seeds were too large to have been blown across modern southern oceans, & apparently they did not floatDrakensburg Mountain in Royal Natal National Park, South Africa The escarpment is capped by resistant basalts, which overlie wind-deposited white sandstone cliffs, both of which are Jurassic and constitute the upper Gondwana rock succession here
Late Paleozoic Life
In the Devonian period, animals & plants developed complex communities on the land as well as in the ocean
Late Paleozoic time was marked by continued expansion of terrestrial forests, as well as further evolution of the marine communities.
By the Carboniferous, the seas were beginning to withdraw, expanding the available habitat for terrestrial life
In the Permian, shallow-marine seas became very restricted and terrestrial deposits made up the bulk of the strata, (Umm Irna Formation in Jordan)
In late Paleozoic, a new environments such coal swamps was originated as a result of sea regression
On late Paleozoic life we will shed the light on the following points: 1. Marine Life 2. Blastoids 3. bryozoan: fenestrate & Archimedes 4. Productids 5. Most of the Devonian fish groups were extinct, but ray-finned fish like shark continued to thrive & were the dominant vertebrate predator 6. The goniatitic ammonoids recovered in the early carboniferous & remained the dominant invertebrate predators 7. Some typical early Paleozoic animals were no longer important: – Graptolite were practically gone. – Trilobite were extremely scar.
Marine Life Although the Late Devonian extinctions affected the reef community and caused widespread extinction in brachiopods and ammonoids, the major phyla of invertebrates soon recovered and remained dominant for the rest of the Paleozoic
During early Carboniferous shallow, warm, tropical waters was dominated by carbonate- producing organisms, such as CrinoidsBlastoids another type of crinoids Pentremites: is a classic index Crinoid fossil of the late
Flower bud-shaped heads of the blastoid Pentremites In life, these heads (1-2 cm in width) would have attached to long stems, like those of crinoids, and these animals would have had a similar filter-feeding mode of life, with tentacles extending from the five petal-like grooves on the topbryozoans Unlike branching bryozoans of Ordovician, the early Carboniferous bryozoan are fenestrate & Archimedes
In addition to crinoids, early Carboniferous witnessed a great abundance of other attached filter feeders, such as the bryozoans Most were delicate, lacy forms “fenestellids” which had hundreds of tiny, filter-feeding animals along lattice work of their skeletonThe most charateristic early Carboniferous bryozoan was Archimedes , fenestellid whose lacy skeleton was arranged around a central spiral ‘corkscrew’ stemThe sea floor was still dominated by brachiopods, but the spirifers had begun to decline, & they were replaced by a group of that dominated the rest of Paleozoic
this group known as Productids, & consists of to shells one concave & the other is flat used as cover for the concave one
Land life
In the late Devonian, the first forests were emerging from the swamp, & diverse arthropods & the first amphibians were living in these forests
During the late Paleozoic, terrestrial life diversified into a much more complex range of communities, with a wide variety of new plants & animals
In the Carboniferous time the coal swamps covering large areas of every continent for the first time in earth history.
Coal never again accumulated to this extent.
The coal were produced by a great variety of plants such as: 1. Spore-bearing plants, the lycopsids produced trees reaching 30m in height, such as Lepidodendron, Sigillaria, & Calamites 2. Seed-plants, such as Conifers, Ginkgoes, Cordaites, & Glossopteris
Animal life in Land Arthropods from Silurian time still inhabit the land The first land Snails & fresh water clams were inhabited the land to the first time in the Carboniferous during the Carboniferous Amphibians were the largest animals in the great coal swamps, by the Permian time it reach 2m long & weighed 130 Kg
Family tree of late Paleozoic amphibians All from the early Permian of TexasTop: Skeleton & reconstruction of one of the earliest known reptiles, Hylonomus, from the Carboniferous of Nova Scotia
Middle: The preservation of fossils, animals were trapped in Sigillaria stems
Bottom: The Amniotic egg of the reptile
The Late Permian Catastrophe
The Permian catastrophe marked the end of an era & rearranged the landscape of life.
The phyla dominant since the late Cambrian, were decimated, & many groups went extinct altogether, 90-95% of all marine species on earth died out
When life recovered millions of years later in the Triassic, a completely new cast of characters recolonized the sea floor
Terrestrial extinctions were also severe
Permian floras show a gradual shift from Cordaites & ferns to conifers, cycads, ginkgoes & other gymnosperms
Terrestrial vertebrates show several waves of extinction as more primitive reptile were replaced by successive waves of more advanced vertebrates
The causes of the catastrophe: 1. Global cooling. 2. the reduction of shallow-marine habitat 3. the basaltic lave eruptions which injected sulfates into the atmosphere 4. The high CO₂ ratio in marine water 5. meteoric impact activity.
The primitive conifer Walchia from the late Pennsylvanian of KansasPermian conifer with slightly broader leaves.
At the close of the Ordovician period, a mass extinction apparently caused by global cooling triggered by Gondwanan glaciation wiped out most of the warm-water invertebrates. So, the Silurian survivors were mostly cold-adapted animals, either from high latitudes or from deep waters
The result was: 1. Early Silurian seas were populated by a low diversity of animals 2. By the Late Silurian & Devonian, life had recovered from the Late Ordovician crisis, & the marine ecosystems that developed were as complex as those of the Ordovician
Marine Communities: after the Ordovician crisis, the major phyla of the Paleozoic fauna returned, but different families & orders dominated, among these : 1. Brachiopods 2. Bivalves & Gastropods 3. Trilobites 4. Cephalopods 5. Eurypterids “ Sea scorpion” 6. Planktonic Organisms 7. The Fishes
Brachiopods
the thin shelled, relatively flat brachiopods (Orthids & Strophomenids) were greatly reduced in numbers & replaced by the much thicker shells & more robust, elongated, deeper bodies brachiopods
During the Silurian the Pentamerids brachiopods were dominant
During the Devonian Pentamerids declined, & the sea floor was taken over by a different group of brachiopods, the Spirifers, the typical Devonian spirifers had very long hinges & , so resembled a pair of wings
The heyday of spirifers was the Devonian, but it survived until the Jurassic
Bivalves & Gastropods continued through the Silurian & Devonian Periods, they were more than brachiopods
Bivalves expanded to fresh water habitats for the first time
Trilobites
Middle Paleozoic trilobites were more specialized than found in the Ordovician
Trilobite were relatively scare in the Silurian
Devonian trilobites included the unusual Phacops, which not only could roll up but also had huge compound eyes
Cephalopods
Nautiloids were declining but they remained one of the major predators in the Silurian
The Nautiloids role as a predator was taken by their descendents the Ammonoids during the Devonian
Ammonoids have a shell that curled into a tight spiral
The suture line in the Nautiloids was a simple curved structure which later it developed into a complex structure (goniatitic) in the Ammonoids, the later suture pattern is typical for late Paleozoic Ammonoids
Eurypterids “ Sea scorpion”
Top predator in Silurian were not Nautiloids or Ammonoids, but the Eurypterids 2.5m length
The eurypterids related to arthropods, ranged through the entire Paleozoic but reached their greatest abundance during the Silurian
Most 13-50cm, but one giant reached 2.5m
Planktonic Organisms
Planktonic organisms also thrived in the warm Silurian & Devonian seas
Acritarchs & Ostracods continued to populate the microplankton as they had since the Cambrian
Graptolites, which were nearly wiped out in the Ordovician extinction, again radiated
Some Silurian graptolites formed either intricate spirals or multiple branches radiating from a single spiral by the late Silurian, free-floating graptolites were in their final decline.
The last known genus Monograptus, the spieces Monograptus uniformis used to recognize the Silurian-devonian boundary
After the end of Silurian, planktonic graptolites become extinct, while the attached bushy type reach the Carboniferous
The Age of Fishes
Simple jaw-less fish had been around for almost 100MY, since the Early Cambrian
During the late Silurian, fish began to diversify, & by the Devonian, they were so abundant in both marine & fresh water deposits that the Devonian is often called “the age of fishes”
Jawless fish continued to be abundant, but during the Silurian, they developed armored head shields and body armor or shield
Placoderms is the typical jawed fish appeared in the Devonian
Jawless fish & the placoderms, not survive the Devonian.
Two other groups of fish that arose in Devonian have living descendants: 1. ray-finned fish, flourished during the late Paleozoic, 99% of the living fishes are from this group 2. lobe-finned fish, have a club-shaped fin supported by stout bones that gave the fin better support; ultimately, this fin allowed the fish to walk on land
Family tree of living & extinct groups of fish
Invasion of the Land
Up until the Ordovician, the land had only sparse plant cover, & soils were probably held in place by microbiotic crusts like fungi, bacteria & algae
In Upper Ordovician deposits, there are fossil spores indicating that more advanced plants were present on land
For a semi aquatic plants to thrive on land, several requirements must be met, such as: 1. A water proof cuticle to prevent desiccation in the dray air 2. A strong supporting structure to lift it off the ground because it can no longer depend on the buoyancy of water 3. A means of passing the sperm to the eggs, which are no longer immersed in water
Although the evidence for land plants in the Ordovician is sparse, the presence of four-parts spores (tetrads) suggested that some from of vascular plants had invaded the moister habitats on land.
In the Early Silurian
the vascular plants were found, these plants have tubes for transporting water & nutrients through the tissues
In Early Devonian, the known Rhynia plant was discovered in the Rhynie chert formation in Scotland
The Rhynia built of simple, leafless stalks with a water proof cuticle & spore-bearing organs called sporangia at their tips, it reach sometimes to half meter tall
The early Devonian plants lacked roots or leaves & were confined to creeping along the ground
Right a reconstruction of Rhynia & its stem showing the vascular tissue (the central zone of the stem) which was relatively inefficient in conducting fluids, so the stems were seldom more than a few centimeters long
By Middle Devonian time
the vascular bundles in a plant such as Psilophyton occupied a large part of the stem, producing a much stronger stalk & more efficient water transport
Early Devonian plant, Psilophyton
These plants evolved roots, both for support & for removal of nutrients out of the soil and water
Living psilophytes are very similar to their Devonian ancestors
By the late Devonian
Lycopsids including the living “club mosses & ground pine” covered the landscape
Some general features of Lycopsids: 1. growing near water. 2. reached meter or more in height, with some carboniferous lycopsid trees reaching 30 m in height 3. have long, slender leaves issued directly from the trunk in a spiral arrangement 4. more advanced than psilophytes, in place of sporangia lycopsids have separate male cone & female cone
Another spore-bearing group of Devonian plants was the Sphenopsids, or jointed- stemmed plants
general features of Sphenopsids: 1. commonly found along stream banks today. 2. have long, hallow stem that jointed. 3. leaves and sporangia clustered at joints
living Lycopodium, in early Devonian they are normally small ground plants, but some were giant trees in the late Paleozoic.
The late Silurian or early Devonian lycopsid Baragwanathia, from Australia
It is one from the oldest known vascular plant fossilsLiving Sphenopsids, Equisetum, known as horsetails or scouring rushes
Another Devonian spore bearing plants are the true Fern, which are: 1. abundant today in any shady, damp area. 2. sporangia occur in small clumps under the leaves 3. there are more than 10,000 living species
In the Devonian time they was small plants but large trees in the Carboniferous time
As a result of the plant invasion of the land, a new habitat was created on land, therefore the land was soon exploited by the first land animals, the Arthropods
In the late Ordovician the land was inhabitant by millipede-like animals
The lower Devonian Rhynie Chert of Scotland contains a number of fossils arthropods as scorpion, spider & mites
By the end of Devonian, the swamps were filled with a variety of crawling, burrowing, & even flying arthropods
Also by the end of Devonian, the first amphibians (land/sea animals) appeared on dry land
From animals such as Ichthyostega transition between lobe-finned fish & typical amphibians was inferred
Head & poison claw of the earliest known late Devonian Centipede 100, the entire animal was about 10 mm longFramework of compound eye from one of the earliest known insects, from late DevonianMillipedes the oldest known land animals, with specimens found in Middle Silurian rocks This specimen from the late Carboniferous of west VirginiaThe oldest known Amphibians, Ichthyostega and Acanthostega found in Upper Devonian rocks of Spitsbergen & Greenland
What led vertebrates to struggle into this new, hostile, dry environment, with no water for support? 1. Some scientists have suggested that they did so because their pools dried up & they had to wriggle across land to find another one 2. They left the water because competition & predation from other fish were much greater there, whereas the land represented an unexploited resource: plenty of arthropods to feed upon & no larger predators
Then its not strange to expect a large event that force the organisms to moved to other environments
Late Devonian Mass Extinctions
The last 2 stages of the Devonian are: – Carboniferous: Famenian & Frasnian
The late Devonian is marked by a severe extinction event, which occurred between the Frasnian & Famenian stages
There is many clues of this extinction 1. In the thick Devonian sequence of New York state, 70% of the marine invertebrate species were wiped out 2. Pentamerids (from Silurian Brachiopods) disappeared completely, 15% of Frasnian brachiopods survived, & ammonoids were devastated 3. Trilobite & Gastropods also declined 4. Tabulate-rugosid-stromatoporid reefs were devastated at the end of Frasnian, & all 3 groups were rare throughout the rest of the Paleozoic 5. The Acritarchs (Microplankton) were almost completely wiped out 6. Most of the typical Devonian fish, including the armored jawless fish & the Placoderms were eliminated
The late Devonian extinction was particularly severe on the great Devonian tabulate-stromatoporid-rugosid reef community
In its place were low-diversity reef built by the cold-water sponge Hydnoceras, suggesting that the Late Devonian extinction was largely caused by global cooling.Devonian Rugose coral Heliophllum, showing a spectrom of growth lines.
The white lines bracket the annual band, & fine lines between are presumed to be daily growth lines: from evidence such as this Paleontologists have deduced that the days were shorter (about 22 hours) & the years had more days about (400)
As in case of late Ordovician extinctions, warm-water marine invertebrates were the most hard-hit by the Devonian extinction
By contrast, polar marine organisms in South America were virtually unaffected
All the above factors point to a global cooling event which supported by the presence of glacial deposits in northern Brazil
Paleoclimate & Paleogeography of middle Paleozoic
Abundance of iron oxides & calcium sulfate evaporites in certain Silurian & Devonian sediments indicates a strongly oxidizing atm
The presence of great organic reef complexes & rich, very diverse marine fossils in both Silurian & Devonian marine strata suggests warm, shallow, agitated seas by analogy with modern shallow tropical seas
Distribution of modern organic reef, major shallow-marine carbonate deposition, & non marine evaporites
Contours indicating latitudinal diversity (number of species) of modern marine planktonic
Foraminefera as function of temperature.
Devonian land plants are similar the world over, suggesting that climate was essentially uniform
Wide distribution of richly fossiliferous middle Paleozoic marine carbonate rocks, & especially the great latitudinal spread of fossil reef suggest subtropical conditions for North America, Europe, Siberia, & Australia
Devonian evaporites also closely parallel the reefs.
Based upon this reasoning, the average climate of the earth through time probably has been milder & more homogenous than it is today, So the present certainly is not a very good key to the past in terms of climate
In this period an explosive radiation of the Paleozoic had been take place, so Ordovician marine life was dramatically different from that of the Cambrian
the difference between Ordovician & Cambrian: 1. diversity: Only 150 families of animals are known from Cambrian, but by the Late Ordovician there were > 400 families 2. diversity is consequence of much greater ecological complexity: The simple Cambrian food chain of deposit-feeding trilobites & a few suspension feeders was replaced by a complex food chain 3. Ecological tiering increased: In Cambrian only few sponges & archaeocyathids protruded more than a few centimeters above the bottom, & in Ordovician several types of organisms reached half a meter or more above the sea floor
Another feature of Ordovician ecosystem was the increase in tiering, or multiple feeding levels above & bellow the sea floor
Cambrian: most invertebrates few cm above sea floor or were very shallow burrowers
Ordovician: crinoids & branching bryozoan began to take advantage of food-bearing currents up to 3m above sea floor
Ordovician life showed a much higher level of ecological complexity than any previous time in geologic history
Examples: Primary producers (algae) grazed by snails
Microscopic plankton fed upon by a wide array of filter feeders
Trilobites scavenged detritus on bottom
The top predators were the giant straight- shelled nautiloids, when they died, nutrients were recycled back into the food chain by bacterial decay
it differ from the inarticulate brachiopods which dominate the Cambrian by: 1. Articulate brachiopods had teeth & sockets in their hinge area to keep the shells better connected, in inarticulate the shells held together by muscles only 2. Articulate shells formed from CaCO₃, while phospate used by inarticulate.
2 groups of Articulate are characterized the Ordovician: 1. Orthids 2. Strophomenids
Bryozoans
colonial animals that form coral-like skeleton with thousands of tiny holes.
Each of these pinhole-sized chambers houses a tiny filter-feeding animal
Crinoids
are echinoderms related to sea stars.
Cambrian stalked echinoderms were primitive animals known as eocrinoids, in Ordovician, they were replaced by the major groups of crinoids typical of rest Paleozoic
about 10m in length, while the largest predator in the Cambrian was 45cm long
By the Early Ordovician nautiolides were abundant worldwide, so the Cambrian Trilobite must have Been a favorite prey item, Therefore the trilobite are much less common in the Ordovician than Cambrian
Snails or gastropods
evolved from the Cambrian Molluscus
Coiled in 2 ways: 1. Plane coiling 2. spiral coiling along axis
Graptolites
their name means ‘written on stone’
in recent years, these animals have been found preserved in 3D in limestone
The late Cambrian graptolites were bushy, branched structures that apparently attached to a hard surface, but Ordovician graptolites were reduced to a few branches & floated on the open ocean
Graptolites was worldwide distributed & evolved rapidly, that why they are the best index fossils in the Ordovician time
Great Radiation
the Ordovician marked a great radiation of many groups of animals
radiation increased the diversity & the ecological complexity of shallow-marine communities
What is causes of great Ordovician radiation which established the Paleozoic fauna? The late Cambrian & Ordovician marked the highest sea levels up to that point (the Ordovician time), This mean, continents was almost completely flooded, forming a large area of shallow seas in which marine life could diversify
O₂ levels increased in the Vendian, Cambrian, & several evidences, & finally reached modern levels (20%) in Ordovician
Ordovician Extinctions
The end of the Ordovician marked one of the most great mass extinction episodes in the history of life
> 100 families of marine animals did not make it into the Silurian
> half the species of brachiopods & bryozoans died out
The Crinoid, stromatoporoid, tabulate, rugosid, receptaculitid reef community was decimated & did not recover until late in the Silurian Period
Nautiloids were also decimated, & trilobites declined even further
Most striking fact about these extinctions: 1. The extinctions were concentrated in tropical groups 2. The survivors & replacements were adapted either to deep waters or to cold waters from high latitudes
Based on the last striking facts, the Ordovician extinctions May resulted from a severe cooling event in the world ocean in the Ordovician, this cause was deduced from the major glaciation of the southern Gondwana super continent, centered in N-Africa
Cooled climate enable only cold-adapted invertebrates could survive to repopulate sea floor in the Silurian
Stratigraphy of the Pre Cambrian & Paleozoic in Jordan
The Pre Cambrian Rocks: Exposed in small area from Jordan, in: 1. Aqaba 2. the eastern rim of Wadi Araba 3. Wadi Rum 4. al Queira area
1Ga, a supercontinent “Rodinia” – formed at the end of the Grenville orogeny
550MY, a supercontinent “Pannotia” – as a result of collisions & dismemberment of Proterozoic supercontinent
these events was indicated by: 1. The Vendian basaltic rocks around the margins of the continent 2. Fault-bounded troughs containing very thick Vendian strata within margins of craton
Reconstruction of Rodina & PannotiaDiagrammatic restoration of Vendian & lower Cambrian strata from California to Utah, suggesting that western N-America was a passive continental trailing edge
Basalt suggest rifting of N-America away from other continent by sea-floor spreadingcross sections showing Vendian & Cambrian strata in SW-United States
breakup of the supercontinents
Sea must have surrounded the continent at first & gradually spread over craton during Late Cambrian & Early Ordovician
Transgression caused by a rise of sea level due to breakup of the supercontinents
The breakup represents fundamental global reorganizations of plate configurations, that’s why we know N-America as it is now
structural modification of Cratons
The broad & gentle warpings of craton – caused by small changes of isostatic equilibrium due to density changes in the underlying lithosphere – have caused formation of: 1. Arches (Raised areas) with thin & less complete sequences of strata interrupted by unconformities 2. Basins (depressed areas) with thicker & more complete sequences, subsided rapidly & received greater & more continuous sedimentary accumulations than Arches 3. faults that may form aulacogens within the outer portion of cratons
Arches Vs Basins
Basins & Arches have greatly influenced the accumulation of oil, gas, salt, gypsum, pure limestone, & other economically important resources associated with sedimentary rock
Cratonic Basins & Arches are 2 types according to the warping time: 1. Warping during sedimentation caused: – Thickening strata in basins – Thinning strata in arches 2. Warping after sedimentation caused thickness patterns superficially
Warping favored accumulation of petroleum, which migrated up-dip from the basin where it was generated
contrast between basins & arches is due only to differential erosion after warping, this warping was too late to trap petroleum
How do we acquire the information for studying broad and & cratonic structures?
As we know much of the evidence for arches lies in the surface outcrops, but only the edges of the basins are exposed, so subsurface information is required to define basins & buried arches
our informational sources was from: Deep drilling for water & petroleum
Deep drilling for H₂O & petroleum provided 3D to our observations geophysical devices; such as magnetic & gravity surveys which revel information about special types & thicknesses of buried rocks
seismology provides the greatest insight into thickness, structure, & in some cases the lithology of buried strata
General features of the earliest Paleozoic sediments
1. The sandstone facies 2. The carbonate facies
The sandstone facies 1. Quartz-rich sand: dominant Cambrian sediment on the craton with glauconite- bearing fine sand, shale was minor – Carbonate sediments replaced all of these during Ordovician times
2. Cambrian cratonic sandstones rank among the most mature in the world – gains: well rounded, sorted, & consists 99% quartz with traces of other stable mineral
3. Ripple marks is a strike feature for the Cambrian sandstone, from ripples feature the origin of the current can be deduced
The carbonate facies By the beginning of Ordovician time, so little land remained exposed that deposition of terrigenous clastic material nearly ceased
Clastic limestone was the main sedimentary deposits, these carbonate show ripple marks, oolites & trace fossils (burrowing action)
All the above features of carbonate indicate the shallow water or tidal origin
typical Upper Cambrian sandstonewell rounded mineral grains: zircon, tourmaline & garnetProfiles of ripple marks of different origins
Early Paleozoic Paleoclimate
Climate evidence from organic reefs, land plants, coal, soil, & O₂ isotope data aren’t available in early Paleozoic strata
the abundance of oolite, some very shelly limestone, & local evaporite deposits do tend to support a warm climate
Presence of wind deposits & scattered evaporites →think of arid deserts
The oldest known fossils consist of filaments of cyanobacteria in rocks about 3.5 Ga
cyanobacteria are – blue green algae – autotrophic, & single-celled – occur in structures called Stromatolites – found in oldest rocks known in Australia – only megascopic fossils from 3.6 Ga – 650Ma
Because heavy meteorite bombardment of the earth to 3.8 Ga, life must have originated in < 300MY After bombardment (about 3.5Ga)
Algae Stromatolites Concentrically layered, domed structures are formed when cyanobacteria trap sediment, then grow upward through sediment layer each day
Today large stromatolites are very unusual occurrence, because most are heavily grazed by a variety of invertebratesone of the oldest known stromatolites, 3.4GaModern filamentous cyanobacterium whose cell are identical in size & shape to the cyanobacterial fossils from Australiafour-celled colonial cyanobacterium surrounded by thick sheath, from cherts in the Ural Mountains, 1.55GaLiving Gloecapsa, cyanobacterium identical in size & shape to the four-celled fossilLiving colonial cyanobacterium
The Origin of Life Ideas
1. Spontaneous generation : The life arise from non-life in the beginning 2. Warm little Pond (Physical condition)
Prior to the microscope, people confused between reproduction & actual origin of life
we must simulate origin of the life via laboratory experiments Because simple early fossils not preserve details of biochemistry
40 years of laboratory work have shown that most basic chemicals of life & even simple cells with many of the properties of life can arise by natural processes اربعون عام من العمل في المختبر اظهرت ان معظم المواد الاساسية للحياة وبعض الخلاية البسيطة التي تحتوي العديد من خصائص الحياة يمكن ان تنشأ بعمليات طبيعة!
Spontaneous generation
Controversy!
Spontaneous generation: The life arise from non-life in the beginning by putrefaction
putrefaction somehow produced metamorphosis of non-living to living matter
Controversy The opinion of those who are not convinced of this idea, why it does not arise today?
In the opinion of the believers in this idea The conditions of earth was changed 1. the modern atmosphere is too corrosive & too oxidizing 2. The early atmosphere had almost no free molecular of O & was rich in the right kinds of chemicals to produce life
Warm little Pond (Physical condition)
Darwin suggested: in some warm little pond, that contain NH₃, phosphoric salts, light, heat, & electricity, protein was chemically formed
Oparin & Haldane proposed: with a reducing atmosphere & abundant CH₄, & NH₃ would have been the ideal soup for the life
The simplest building blocks of life, can easily be produced in laboratory experiments such as amino acids (form proteins),fatty acids (form fats, or lipids), & sugars
Other experiments show that droplets of proteins can condense, surrounded by a lipid membrane, to form proteinoids with very lifelike properties
Carl Woese has found 2 types of bacteria came from the universal ancestors: 1. Archaebacteria: live on H-sulfide, CH₄, or extremely hot salty spring 2. Eubacteria or true bacteria: most familiar bacteria & cyanobacteria
Family tree of life based on molecular similarities of RNA
Part.2 : Cambrian Explosion!
The Cells
Prokaryotescell: without nucleus or organelles (sub-cellular structures) & reproduced by simple cell division
Eukaryotes cell: with nucleus & organelles appeared in late Precambrian
Multicellular animals (metazoans) are known as trace fossils, tracks or trials of worm-like creatures
Ediacaran fossils: earliest animal fossils, not related to later groups, found in Paleozoic – such as soft bodied animals, resemble jellyfish, sea pens, & wormlike – Ediacaran called Vendozoa because clearly unrelated to anything living today – represent multicellular & metazoan – dominated in the Vendian 600-544 Ma
The complex Ediacaran metazoan fossils, from the Ediacara Hills, S-Australia A: wormlike creature (a meter in length) B: more elongated wormlike form C: linked to arthropods
Cambrian explosion
The sudden appearance of species belonging to several of the main divisions of the animal kingdom in the cambrian rocks was great problem for Darwin الظهور المفاجئ للانواع التي تنتمي للعديد من التقسيمات الرئيسية لمملكة الحيوانات في الصخور الحفرية المعروفة – التي تعود الى الكامبري – شكلت مشكلة لنظرية التطور Simply the problem was the appearance of richly fossiliferous Cambrian strata full of trilobites were underlain by seemingly barren Precambrian rocks المشكلة هي ظهور مستحاثات الترايلوبايتس – ثلاثية الفصوص – وتحتها طبقات خالية من حلقة وصل، اي تدل على ظهور مفاجئ لهذه المخلوقات ولا يوجد تطور لها من سلف
Did life originate abruptly, or was there hidden somewhere an undiscovered fossil record of the transition to multicellular life? هل نشأت الحياة بشكل مفاجئ ام هناك احفوريات غير مكتشفة؟
S. Tyler found microfossils from 2Ga rocks
After Tyler, Barghoorn, & Schopf has 1. documented microfossil localities 2. shown that single-celled organisms dominated the earth from 3.5Ga to 600Ma
R. Sprigg found jellyfish in Ediacara Hills
Australian paleontologists collect more of jellyfish fossils, provides clear evidence of soft bodied animals that predated Cambrian, they represent multicellular animal & metazoan العثور على قناديل البحر وفر دليل على اجسام رخوة عاشت قبل الكامبري لان قناديل البحر متعددة الخلاية jellyfish fossils are known as Ediacaran fossils dominated the world in Vendian 600-544 Ma, because found in many places such as England, China, Scandinavia, Russia
Part.3 : Cambrian Organisms
Shelly, Invertebrates
3.5Ga – 600Ma the world was dominated by stromatolites & microfossils (such as acritarchs) which declined about 675Ma
600Ma – 550Ma the world was dominated by the Ediacaran soft bodied forms such as jellyfish, Except for some tiny, tube-shaped fossils made of calcite
Early in the Cambrian 1. Vendian animals disappeared completely & were replaced by little shelly fossils 2. Cambrian strata yield burrowing in the sediments, which mean that complex worms, & tube like bodies was found
Shells were the harbingers of the abundant shelled invertebrates found later in the Cambrian
Fossils from the lowest CambrianVendian & lower Cambrian strata transition from the soft bodied metazoans to complex skeletonized invertebrates!
Logical thinking!
What triggered replacement of microfossils by soft-bodied animals in Vendian? What triggered replacement of soft-bodied animals by shelly in Cambrian?
The extinction of the late Proterozoic by glacial event about 600Ma
OxygenConcentration (in Vendian 6-10%) limited O₂ was the critical factor preventing the evolution of multicellular life for 3Ga – O₂ reached modern level in late Cambrian, so hard CaCO₃ shelled organisms start to appear – Organisms cannot secrete CaCO₃ until the O₂ level reaches a critical, this explain why earliest shelly fossils are mostly calcite or phosphatic tubes
Tectonic change, Rifting, & Volcanic activityin latest Proterozoic A. produced transgression which expanded the area of shallow marine shelf available for life B. released many of N₂ & C into shallow- marine, where shell use them
Increased N₂ provide materials for animals to build hard shells, mostly calcite – hard shell used by animals for protection
The shallow marine world was once covered with thick cyanobacterial mats, but in the early Cambrian they nearly disappeared – The appearance of the small shelly fossils & deep burrows are correlated with this decline in stromatolites (cyanobacteria) – Before the appearance of small invertebrate animals, nothing fed on cyanobacterial mats – Some of these small shelly fossils is primitive molluscus that grazed & cropped stromatolites – Once these shelly animals evolved, they would have a virtually unlimited food source – stromatolites survive today only in environments that are hostile to grazing invertebrates (lagoons environment) which is too salty for grazing snails to live in
Diversification of invertebrates led to even more complex ecological relationships, such as predation. – By the middle Cambrian time, there is evidence of large predators, which reached half a meter – trilobites with healed bite marks, but many Cambrian animals have spiky or platy armor as devices to thwart the predators. – the appearance of predators represents a more complex food chain as well as from producer (plants) to feeder
Cambrian fauna
Arthropods: the jointed legged phylum of animals that includes insects, spiders, scorpion, crabs, & other kinds of animals
Archaeocyathids: strange group of organisms shaped like double-walled ice cream cones, & They are 25mm in diameter & up to 150 mm high, but some can reach 1m in length
Brachiopods: These animals have 2 clam-like shells joined for protection
Molluscs
Echinoderms or spiny skinned animals
Arthropods The most famous fossils from this phylum are the trilobites, these fossils was well preserved due to the skeleton composition, which consists of calcite & organic chitin
Modern arthropods skeletons composed of only chitin, that’s why its not found as fossils
In Cambrian seas the trilobites evolved so rapidly around the world, so they used as tool of correlation
> 600 species are known from the Cambrian, but they ended by the Ordovician
Trilobite burrows & feeding tracks are among the most common trace fossils of the CambrianArchaeocyathids A-I Early Cambrian Archaeocyathids J-k inarticulate brachiopods L-O Archaic molluscus P eocrinoid, replaced by crinoid in Ordo.Brachiopods A long, fleshy stack called a pedicle extends through the hing area & helps the animal burrow are attach to hard surfaces inarticulate: earliest Cambrian brachiopods Most inarticulate brachiopods have shells of chitin & phospateMolluscs Today represented by clams & snails, By the middle Cambrian snails & clams had evolved, but they remained rare until the OrdovicianEchinoderms or spiny skinned animals Today they are represented by starfish, crinoids, & cucumbers
Most are built of calcite plates All living echinoderms are built on a pattern of 5-fold symmetry, such 5 arms on starfish
Cambrian echinoderms have no living representativesHeicoplacus Show no Similarity with living ecinoderms represent primitive type from lower Camb.
When the Cambrian fauna examine the following note will be clear
Most of the animals were extremely primitive forms which not survive, many of them represents an early stages of their phyla evolution, so after each evolution stage the old stage pushed aside or extinct.
Ecological communities were very simple Ex. The stromatolite, cyanobacteria, archaeocyathid, included only a few burrowers, mostly worms & inarticulate brachiopods
It seems from all the information which discussed till now about Cambrian fauna, that Cambrian life simple & monotonous
But the Burgess Shale fauna which discovered in the Rocky Mountains near Field, British Columbia showing that Cambrian world was much richer than what we imagined
Cambrian life
Cambrian life include At least 20 types of Arthropods with body designs fundamentally different from those of any living arthropod
A number of wormlike animals At least 50 other kinds of animals that cannot fit into any living phylum of invertebrates
So each type of the Cambrian organisms represents a different version of metazoan design that has not survived
So the Cambrian had diversity comparable to that of later periods, but with an important difference: almost all this diversity is in primitive forms, each of which would represent different phylum or class in a modern classification
By contrast, from the Ordovician onward, most fossils fit into about 8 phyla, & just a few classes & orders within these phyla account for most species
ARCHEAN EON Each continent contains pieces of the Earth’s oldest crust referred to as shields
Cryptozoic Rocks
Importance of cryptozoic rocks: 1. major source of Cu, Cr, Au, Ag, Fe, Ni, U 2. Half of word metallic mineral resources
cryptozoic rocks characterized by: 1. lacking index fossils, except for some microscopic cyanobacterial fossils 2. are severely deformed, metamorphosed & deeply eroded
Some of the oldest dated rocks in the world (3.8Ga) occur near Greenland
Cryptozoic Chronology
Sedgwick in Wales The Canadian Shield
The chronology or dating of cryptozoic rocks was established by isotopes
Sedgwick in Wales
Sedgwick recognized clearly the relationships between older unfossiliferous rocks & fossiliferous early Paleozoic ones in Wales
Based on relationships between unfossiliferous & fossiliferous rocks Sedgwick named: 1. Azoic ‘no life’: first name for Precambrian 2. Eozoic & Archeozoic ‘ancient life’ 3. Cryptozoic ‘obscure life’ was proposed After the fossils were found
The Precambrian-Paleozoicboundary 1. Precambrian rocks are more deformed & metamorphosed than the overlain Paleozoic 2. unconformity between 2 rock sequences 3. Lowest stratigraphic appearance of cambrian index fossils has defined boundary 4. today this boundary defined by isotopes
The Canadian Shield
Cryptozoic rocks first recognized in Britain, N-America, & Scandinavia
The cryptozoic rocks are most widely exposed in the stable continental Cratons or Shield
The shield concept comes out from the appearance of these rocks on the geologic map, while the shields are largely accidents of erosion where the stripping off of later deposits has exposed the ancient basement
Tectonic term Craton is more useful than shield because it defines the overall relative structural stability of a large portion of the earths crust through a long time regardless of the age of the rocks exposed there today
Cryptozoic & earliest Paleozoic isotopic-data provinces of basement rocks of continents
Interpretation of Crustal development from Sediments
The sources from which sedimentary rocks were derived are reflected by composition
Composition modified after deposition by 1. Climatic condition 2. Chemical changes
Type of sediments 1. Terrigenous clastic: derived from erosion of older rock, contain silicate such as quartz 2. Non-terrigenous: formed in aqueous depositional environments – Chemically precipitated sediments, such as the evaporites & carbonate rocks composed of fossils skeletal or calcareous particles
Textural Maturity
Clastic textures reflect: 1. rates of physical sedimentary processes 2. intensities of sedimentary processes
Grain size or coarseness reflects the power of transporting agents
Transporting agents 1. Wind: moves only sand & silt 2. Moving water: carry sand, silt & gravel 3. Mudflows & Glaciers: carry sand, silt, gravel, large blocks for along distances due to grater density & viscosity
Grain Size decreases with time & distance of transport, Because 1. decreasing carrying power with distance 2. reduction of particle size by abrasion
Size Sorting: Range of sizes, depend on: 1. time of transport 2. constancy of physical energy of agents
Rounding of fragments is related to: 1. intensity & duration of abrasion 2. toughness of materials (clasts)
High abrasion & winnowing cause: 1. size of particles will be reduced 2. sorting of size will improve 3. rounding will increase
Sediment in long & constant agitation (beach sand) are well sorted, due to early dropping out of large particles & removal or winnowing away of fine materials, So: 1. deposition of gravel near the source 2. well-sorted sand in other place, sea ward 3. well-sorted particles of fine silt & clay in a third place, more deep waterclastic sediments become finer as they are moved farther from their source development of textural maturity of sand via abrasion & separation or sorting
Compositional Maturity
Mineral composition of a clastic sediment will change as its particles are subjected to: 1. repeated physical crushing 2. chemical destruction of less stable mineral
Rock fragments tend to be ground down rapidly to their separate mineral grains 1. Dark minerals (pyroxenes & amphiboles) → rapid chemical breakdown 2. The more stable mineral will stay & reach the ultimate residue such as quartz, feldspar, some mica, & heavy mineral (such as zircon, garnet, magnetite)
Ultimate residue composition depend on: 1. Resistance of the original components 2. Abundance of the original components
Typical changes via time of composition of sand that derived from erosion of granitic Less stable minerals are broken down both physically & chemically to leave a residue of most resistant mineral grains
Stratification
provides clues about depositional processes
Thin & horizontal lamination in very fine sediments – formed by slow settling of clay & silt – need a minimum of current agitation – best environment: deep lake, sea bottom
Cross-stratification common feature of sands & fine gravels deposited by wind or water
Cross-stratification formed by moderately strong & turbulent traction currents that roll, bounce particles over a loose sediment surface corrugated by small-scale ripples or larger-scale dunes, Grains carried to the crests of the ripple or dune roll or slide down the steeper side, so resulting inclined cross-stratification reflects the steeper face of the migrated ripple or dune, & it dips toward the down current direction
Ripple marks in Proterozoic quartzite Ripples exposed on 3 different stratification planes: on middle surface perpendicular in trend to the others, indicating 90˚ shift of wave & current directions between times of deposition of strataOrigin of cross-stratification by migration of ripples or dunes produced by vigorous bottom currents
Grains roll & bounce over the dune crest, coming to rest on the steeper faces
Successive inclined or cross-stratification forms as the steeper face migrates, each lamina is a buried fossil steeper faceComparison of sorting of sand grains sizes by different sedimentary processes Sorting helps in determining the origin of an ancient sandstone, Ex. note great difference of sorting by surf & turbidity currents
Proterozoic Rocks Record
First 100Ma: no record is knowndue to 1. the surface was volcanic 2. intense bombardment by meteorites
3.9 Ga: local crustal blocks formed after 1. heat began to dissipate 2. large meteorite impacts ceased or stopped
4 – 2.5Ga: Oldest rocks, are 2 assemblages 1. Greenstone belts: metamorphosed-volcanic rocks, associated with sediments – drives from dark, & green-colored minerals produced by metamorphism of mafic rocks 2. Gneiss belts: high-grade metamorphic
Relation between assemblages isn’t clear: – First view: they differ only in degrees of metamorphism & reconstitution – other: 1. Gneiss is remnants of incipient continents 2. greenstone remnants of oceans & volcanic arcs formed between continents
The Proterozoic sediments are: 1. Poorly sorted graywackes 2. Light-colored, & well-sorted pure quartz sandstones that show cross-strata, ripple mark 4. well-rounded quartz/chert pebble 3. limestone, contain stromatolites
stromatolites wavy laminated structure, formed by cyanobacteria
Stromatolitic reef structure from 1.6 Ga
Ocean & Atmosphere
Archean rocks bear evidence of anaerobic early conditions, that was supported geologically by many clues, such as : 1. Sediments are dark-colored due to the presence of unoxidized carbon, fine iron sulfide FeS₂ & iron carbonate FeCO₃ 2. Rocks contain several metals with affinities for O: Mn, Cu, Zi, U, & vanadium, which present widely in least oxidized state 3. Sulfur has an affinity for O but it present only in its unoxidized or reduced state in the pyrite FeS₂ 4. Differences between sulfur isotopes in Archean & Proterozoic sediments were thought to reflect a contrast in atm O content
The Archean chemical sinks consumed any available early O, this was by oxidation of hydrogen H₂O & carbon CO₂
After these sinks were full saturated with O, S, Fe, & other metals begin to be oxidized, this was indicated by red color of oxidized iron & sulfur CaSO₄
It was inferred that this saturation occurred sometime after photosynthetic organisms appeared & began to release O₂ into atm
Appearance of widespread, red-colored strata “red beds” among Proterozoic rocks seemed to confirm a gradual accumulation of free O₂
Geologic evidence mentioned above cited or indicated that the Archean condition was aerobic, this view is fit to the biochemists, But some biologist argued that the free O₂ should be at the same time generated to the atm since the photosynthesis began, so they think that no need to one Ga which was suggested by geologist for the consumed O₂ by the chemical sinks
A growing number of geologist have challenged the slow-accumulation of free O₂ on the following ground : 1. The unoxidized C in Archean sediments may not be significantly different, either in total abundance or in isotopic makeup, from C in younger ones 2. Free C as well as Fe-sulfide & Fe-carbonate minerals have been preserved in O-poor muddy environments (such swamps) right up to the present day 3. Unoxidized Mn, Cu, Zn, vanadium, U although widely scattered, not very common in Archean sediments & like free C & Fe sulfide, might be explained by local anaerobic conditions of deposition 4. Some Archean red beds & oxidized sulfate evaporites have now been discovered, as well as some oxidized Archean soils So. significant free O₂ existed even in the Archean atmosphere
Cryptozoic Climate
Evidence about cryptozoic climates is scant, but there is nothing that indicates conditions different from later geologic time
Chemical arguments suggest more atm CO₂, a condition that should have caused a warmer average global T (greenhouse effect) & more acidic rains
direct evidence of climatic extremes: 1. Evaporite deposits & mud cracks attest to dray & probably hot conditions sufficient to completely evaporite sea-water locally 2. Proterozoic wind deposits also are known, & they suggest large desert dune fields 3. Evidence of cold periods is even better known by glaciers deposits
Mud cracks in red shale
rocks such as these, along with salt crystals, show that hot, dry conditions were common 1.8 Ga & that enough free O₂ was present in the atm to turn the sediments rusty red
Early Proterozoic Glaciation
As a strong indicator for cold conditions coming from sediments, were Gowganda Formation in Ontario show the following features of the sediments: 1. massive rock type 2. unstratified & unsorted large boulders, pebbles, sand, & fine clay surrounded by a fin matrix of dark material 3. laminated mudstone, resembles Pleistocene glacial lake clays containing laminae interpreted as seasonal layers, & some of layers contain scattered pebbles 4. at several localities where the surface is exposed, fine, parallel scratches are visible, which strongly resemble striations made by glaciers
All of these features which had been seen in the Gowganda Formation are direct clues for glaciers deposits or moraine
Laminated mudstone with scattered pebbles & sand grains dropped from above
Association with glacial tills suggest dropping of sandstones from drifting icebergs
Late Proterozoic Glaciation
The end of the Proterozoic was marked by a great global glaciation event, the Varangian glaciation, which produced continental glaciers at nearly equatorial latitudes
The exact causes of this extraordinary glaciation are controversial, but the planet nearly became a lifeless frozen world, like Mars
When the Varangian glaciers retreated, multicellular life emerged for first time after nearly 3Ga of single-celled life on this planet
Global distribution of late Proterozoic (Varangian) glacial deposits (triangles), showing their occurrence in ancient equatorial regions
In some places, these glacial deposits are interbedded with marine limestone, further proving their low-latitude origin
Such evidence leads some scientists to suggest that the earth my have barely avoided freezing over completely in the Varangian