1. Geologic Time

2. Geologic Time Scale
The appearance and disappearance of different organisms give us the ‘markers’ for dividing Earth’s history into basic units of time.
These units or divisions are also based upon geologic changes in Earth’s appearance.

3. Therefore,
The different periods of geologic time are based upon the life forms that dominated during that period.

4. Different Life Forms Jurassic Period  dinosaurs dominate
Cretaceous Period  birds appear
Eocene Epoch  bats & whales appear

5. Geologic Time Scale You are here. Eras are divided into 
Periods,,, Periods are divided into 
Epochs… Epochs are divided into 
You are here.

6. Present 
MYA = Million Years Ago
Past 

7. Geologic Eras
Paleozoic Era: Followed the Precambrian time and is characterized by the land masses forming Pangaea and a rich fossil record.
Mesozoic Era: Called the Age of the Reptiles, Pangaea broke up and the Sierra Nevada mountains were formed.

8. Cenozoic Era: current era that we live in and called the Age of Mammals.

9. -----------Mesozoic Era------------
Triassic Jurassic Cretaceous

10. Mass Extinctions
The Earth has been through five different mass extinction events.
Mass extinction has resulted in the elimination of most species on Earth.
The last one was 65 million years ago and resulted in the death of the dinosaurs.

12. Precambrian vs. Cambrian time
The time between the formation of the Earth and about 542 million years ago is called the Precambrian time.
The Cambrian time is the time following the Precambrian time when there was an explosion of plants and animals.

13. Cambrian Time
12 %
Precambrian Time

14. The End