Geologic Time Scale

Chapter 17

Formation of Earth

• 4.6 billion years old• Took 100 million years to form

Formation of Earth

• Early atmosphere: CO2, CO, H2O, N2, H2S, but no O2!

• First life was simple one celled prokaryotes about 3.5 mya

Miller and Urey

• Experiment simulated Earth’s early atmosphere

• Created organic compounds necessary for life—amino acids

Geologic Time Scale

• Used by paleontologists• Represents evolutionary time• Mark major changes in fossils

Cen

ozoi

c Er

a

• Quaternary Period• 1.8-present• Glaciations, mammals increased, humans

• Tertiary Period• 65-1.8• Mammals diversified, grasses

Mes

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c Er

a • Cretaceous Period• 145-65• Aquatic reptiles diversified, flowering plants,

mass extinction• Jurassic Period

• 208-145• Dinosaurs diversified, birds

• Triassic Period• 245-208• Dinosaurs, small mammals, cone-bearing

plants

Pale

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a• Permian Period

• 290-245 Reptiles diversified; seed plants; mass extinction

• Carboniferous Period• 360-290 Reptiles; winged insects diversified; coal swamps

• Devonian Period• 410-360 Fishes diversified; land vertebrates (prim amphibs)

• Silurian Period• 440-410 Land plants; land animals (arthropods)

• Ordovician Period• 505-440 Aquatic arthropods; mollusks; vertebrates (jawless

• Cambrian Period fishes)• 544-505 Marine inverts diversified; most animal phyla

evolved

Prec

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Tim

e • Vendian Period• 650-544• Anaerobic, then photosynthetic prokaryotes;

eukaryotes, then multicellular life