Geologic Time Scale Chapter 17

Formation of Earth 4.6 billion years old Took 100 million years to form

Formation of Earth Early atmosphere: CO 2, CO, H 2 O, N 2, H 2 S, but no O 2 ! 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

Cenozoic Era Quaternary Period 1.8-present Glaciations, mammals increased, humans Tertiary Period Mammals diversified, grasses

Mesozoic Era Cretaceous Period Aquatic reptiles diversified, flowering plants, mass extinction Jurassic Period Dinosaurs diversified, birds Triassic Period Dinosaurs, small mammals, cone-bearing plants

Paleozoic Era Permian Period Reptiles diversified; seed plants; mass extinction Carboniferous Period Reptiles; winged insects diversified; coal swamps Devonian Period Fishes diversified; land vertebrates (prim amphibs) Silurian Period Land plants; land animals (arthropods) Ordovician Period Aquatic arthropods; mollusks; vertebrates (jawless Cambrian Period fishes) Marine inverts diversified; most animal phyla evolved

Precambrian Time Vendian Period Anaerobic, then photosynthetic prokaryotes; eukaryotes, then multicellular life