History of Life

I. Early Earth Hot, volcanoes, very little oxygen but a lot of water vapor Once Earth cooled the water vapor condensed to rain (a lot!!!) 3.9 -3.5 billion years ago the 1st organisms appeared 90% of all species that have lived on Earth are extinct Fossils – foot prints, imprints, molds, amber, frozen, cast, and petrified Paleontologist –people that study ancient life

II. Dating Fossils Relative dating Radiometric Dating Older rocks and fossils make up the deeper layers Problem: Earthquakes mix up layers Radiometric Dating Use radioactive isotopes that break down over a known amount of time (like a clock) Very old fossils – use potassium 40 which turns into argon (half life of 1.3 billion years) Young fossils- use Carbon 14 (half life of 5730 years)

III. Geological Time Scale 4 Eras Precambrian – longest and oldest 3.5 billion to 544 million years ago Started with bacteria, then eukaryotes, then simple animals (sponges and jellyfish) Paleozoic – explosion of life 544 million to 245 million years ago Oceans had worms, starfish and fish Land had ferns, other plants, amphibians and reptiles

Mesozoic Cenozoic 3 periods (Triassic, Jurassic and Cretaceous) 245 million to 66 million years ago Dinosaurs, birds, some mammals and flowering plants Mass extinction occurred Pangaea broke apart Cenozoic 66 million to present Mammals flourish, primates and humans