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 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
66 mya---
245 mya---
Precambrian
Until 544 million years ago
Unicellular prokaryotes
Multicellular eukaryotes
544 mya---

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

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