Summary, Part 1

The oldest known fossils consist of filaments of cyanobacteria in rocks about 3.5 Ga

cyanobacteria blue green algae, autotrophic, single-celled, occur in stromatolites structures, found in oldest rocks known in Australia 3.5Ga

cyanobacteria are the only megascopic fossils in rocks from > 3.6 Ga to 650MY

life must have originated in about 3.5Ga Because heavy meteorite bombardment of the earth to 3.8 Ga

The Origin of Life Ideas
1. Spontaneous generation: The life arise from non-life in the beginning by putrefaction & the conditions changes now to allow it today (atm too corrosive & oxidized & the ancent atm had no free of O molecules)
2. Warm little Pond (Physical condition) Darwin’s Theory (in warm little Pond that contain heat, electricity, ammonia, phosphotic salt, & light can produce protein)
3. Soup theory : Oparin & Haldane, with a reducing atm & abundant CH₄, & NH₃ would have been the ideal soup for the origin of life

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

Summary, Part 2

Prokaryotic cell without nucleus or organelles (sub-cellular structures) & reproduced by 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
– dominated in the Vendian 600-544 Ma
– soft bodies, jellyfish, sea pens, wormlike
– called Vendozoa, not related to later groups
–  represent multicellular & metazoan

Cambrian explosion The sudden appearance of complex organisms (Trilobites) in late Precambrian

S. Tyler found microfossils from 2Ga rocks

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

jellyfish fossils provides evidence of soft bodied animals that predated Cambrian, they represent multicellular animal & metazoan

single-celled & Microfossils dominated the earth from 3.5Ga to 600Ma
jellyfish (Ediacaran) dominated the world in Vendian 600-544 Ma

Symmetry, Part 3

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

Microfossils replaced by soft-bodied animals in Vendian, & soft-bodied animals replaced by shelly in Cambrian

Life evolution hypotheses
The extinction of the late Proterozoic by glacial event about 600Ma
Oxygen Concentration (in Vendian 6-10% & in Cambrian 20%) limited O₂ was the critical factor preventing the evolution of for 3Ga
tectonic change, rifting, & volcanic activity in latest Proterozoic, produced transgression which expanded the area of shallow marine shelf available for life & released many of N₂ & C into shallow-marine
Increased N₂ provide materials for animals to build hard shells (for protection), calcite
Shallow marine covered by cyanobacterial but in early Cambrian they disappeared due to appearance of shelly fossils & deep burrows that grazed & cropped stromatolites
Diversification of invertebrates led to more complex ecological relationships, predation
– predation such as trilobites & many 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

Organisms cannot secrete CaCO₃ until the O₂ level reaches a critical, this explain why earliest shelly fossils are mostly calcite or phosphatic tubes

Cambrian fauna
Arthropods: the jointed legged phylum of animals that includes insects, spiders, scorpion, crabs, & trilobites
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 represented by clams & snails (middle Cambrian, rare until Ordovician)
Echinoderms or spiny skinned animals represented by starfish, crinoids, & cucumbers
– Most are built of calcite plates
– have 5-fold symmetry (5 arms on starfish)

trilobites 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 Cambrian

Heicoplacus
Show no Similarity with living ecinoderms
represent primitive type from lower Cambrian

Cambrian life include
1. At least 20 types of Arthropods
2. A number of wormlike animals
3. At least 50 kinds of animals that cannot fit into any living phylum of invertebrates

each type of Cambrian organisms represents a different version of metazoan

from the Ordovician onward, most fossils fit into about 8 phyla

The End