1. History of Life

2. 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!!!)
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

3. 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)

4. 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

5. 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