I. What was it like on early Earth ? Very hot Meteorites colliding into earth Frequent volcanic activity Atmosphere with little oxygen & lots of nitrogen & carbon dioxide

Approximately 3.9 billion years ago the earth cooled & the water vapor in the atmosphere condensed - creating the earth’s oceans.

scientists believe the first organisms appeared.

Calendar of Earth’s history based on evidence found in rocks. Earth began in the Precambrian era. We live in the Cenozoic Era.

4.5 billion years ago to 550 million years ago 87% of Earth’s history Prokaryotes begin –bacteria Eukaryotes begin– multicellular organisms

550 to 245 million years ago Beginning of fish, plants &reptiles Largest mass extinction in the fossil record was at the end of this era

245 to 66 million years ago Beginning of dinosaurs, mammals, flowering plants, birds Mass extinction causing the dinosaurs to die at the end of this era –due to a meteor collision?

66 million years ago to present day Beginning of complex mammals Humans evolve

Summary How old do scientists believe the earth to be? How has life on earth changed from then to now?

13. Gradualism Organisms evolve in a process of slow and constant change

14. Punctuated Equilibrium The idea that species evolve in short bursts, and then go through long periods with little evolution.