Fossils and Geologic Time

1. Fossils and Geologic Time

2. Early History of Earth Hot interior and surface Volcanoes released gases Water vapor Carbon dioxide Nitrogen Mot much oxygen First organisms 3.9 billion years ago

3. Fossils – Clues to the Past A fossil is evidence of an organism that lived long ago. trace cast petrified imprint mold amber

4. Fossils – Clues to the Past How do fossils form? Animal or plant covered in mud or sand Minerals seep into the body Pressure turns mud or sand into rock

5. Fossils – Clues to the Past How do we know how old fossils are? 1. Relative dating – Rock forms in layers Younger layers at top Tells us which fossils are older or younger

6. Fossils – Clues to the Past How do we know how old fossils are? 2. Radiometric Dating – Rocks have radioactive isotopes – unstable atoms that break down over time We know how long it takes to break down Absolute age

7. Geologic Time Scale A calendar of Earth’s history based on fossils 66 mya--- 245 mya--- 544 mya---

8. Geologic Time Scale Precambrian Until 544 million years ago Unicellular prokaryotes Multicellular eukaryotes 66 mya--- 245 mya--- 544 mya---

9. Geologic Time Scale Paleozoic 544 to 245 million years ago Fish, land plants, amphibians, reptiles Ends with mass extinction 66 mya--- 245 mya--- 544 mya---

10. Geologic Time Scale Mesozoic 245 to 66 million years ago Small mammals, dinosaurs, birds Mass extinction 66 mya--- 245 mya--- 544 mya---

11. Geologic Time Scale Cenozoic 66 million years ago to today Mammals 66 mya--- 245 mya--- 544 mya---

12. Continental Drift Pangaea 245 million years ago Breaks up 135 million years ago Moving apart 66 million years ago