Geologic Time Scale How We Know About Our

Geologic Time Scale How We Know About Our Past

Divisions of Geologic Time • Eon – there are 3 –Archean and Proterozoic (Pre. Cambrian) –Phanerozoic (Cambrian) • Era (no eras before Cambrian) • Period • Epoch

Four Major Divisions of Time • Pre-Cambrian – simple marine life • Paleozoic – invertebrates • Mesozoic – dinosaurs & reptiles • Cenozoic – mammals

Pre-Cambrian Era • 4. 6 bya to 544 mya • Longest unit of geologic time • Not much known • Sponge fossil record –Deeply buried and changed by heat and pressure

Pre-Cambrian Era (cont’d. ) • Cyanobacteria – produced oxygen • Ozone began forming • Soft bodied simple organisms like jellyfish existed

Paleozoic Era • 544 mya to 245 mya • Warm shallow seas • Marine life forms –Trilobites, Brachiopods, & Crinoids • Pangaea forms

Paleozoic Era (cont’d. ) • Fish appeared • Appalachian Mountains formed • Plant & Animal life moved to land • Mass extinctions, tectonic activity & glaciers

Mesozoic Era • 245 mya to 65 mya • Dinosaurs & reptiles dominate • Birds appear • Little mammals (non-dominant) • Pine trees and flowering plants • Pangaea breaks up

Cenozoic Era • 65 mya to present • Dinosaurs become extinct • Climate cools; ice ages occur • THE AGE OF MAMMALS