1. Early History on Earth

2. Formed ~ 4.6 billion years ago (bya) Widely accepted ideas: –Earth = hot ball of rock –Bombarded w/ meteorites –Many volcanoes that shot out gases

3. Cooled down ~ 3.9 bya Cool enough for water vapor to condense Violent rainstorms Early Atmosphere had no Oxygen

4. Oceans formed ~ 3.5 bya First living organisms may have lived here First Fossils are about 3.5 Billion years old

5. First Fossils Stromatolites Cyanobcateria

6. Fossils: Any evidence of an organism that lived long ago Casts & Molds Trace fossils Amber fossils Frozen fossils Petrified fossils Imprints

7. Fossils are usually found in sedimentary rock Organism died and sunk to bottom of a body of H 2 O Water carries sediments, which pile onto body Carcass is buried under compressed sands, etc. Carcass is sometimes well-preserved under layers Fossil is brought to surface by geologic processes Paleontologist discovers fossil

8. Paleontologist: studies fossils to learn about Earth’s history What kinds of organisms lived here? What was their behavior like? What were the climate & weather like? What was geography like?