1. 2014
Mrs. Hughes
8th Grade Science
Geologic Time
Shows Earth’s History

2. Uniformitarianism Earth is an always changing place
The same forces of change at work today were at work in the past
The Earth has changed gradually (very slow)

3. The Geologic Time Scale
Shows Earth’s History divided into time units based on life forms that existed and major events.

4. Earth is estimated to be 4.6 billion years old.
Oldest living things were one-celled organisms at about 3.5 billion years.
Humans show up only about 100,000 years ago.

5. Division of Geologic Time
Eons – largest unit
Eras – eons are divided into eras
Paleozoic, Mesozoic, Cenozoic
Periods – eras are divided into periods
Epochs – periods are divided into epochs

6. Precambrian Time The longest part of Earth’s history
About 4.5 billion years.
1st rocks formed 3.9 billions years ago.
1st living things appear about 3.5 billion years ago during the Precambrian; single-celled simple organisms (bacteria) .

7. Precambrian Time
Invertebrate (no backbone) animals show up at the end of the Precambrian.
This time ended with a global ice age.

8. Paleozoic Era 544 mya – 248 mya
Means “ancient life” often known as the age of fish.
At the beginning of this era there is an explosion of life in the warm, shallow seas of the time.
Organisms with shells and vertebrates (backbone) form.
Trilobites, mollusks, fish, amphibians

9. Paleozoic Era
Life moves onto land at the end of this era and the first reptiles and large insects form.
Appalachian mountains form.
Pangaea forms. .

10. Paleozioc Era
Largest mass extinction marks the end of this era. 95% of all life disappears in the fossil record
One theory is global – climate change due to massive volcanoes

11. Mesozoic Era 248 mya – 65 mya
Means “middle life” and often know as the age of reptiles.
Dinosaurs ruled the Earth
First flowering plants
First birds and mammals
Pangaea separates

12. Mesozoic Era Another mass extinction at the end of this era.
Most excepted theory is a massive asteroid hit the Earth causing global-climate change.

13. Cenozoic Era 65 mya - present
Means “recent life” and known as the age of mammals
Several ice ages
Fossils of the 1st humans show up 100,000 years ago. (not very long ago in geologic time)

14. Quick Check
1. ____ is the idea that the forces that changes the Earth today are the same forces that existed in the past.
A. Paleontology
B. Uniformitarianism
C. Cambrianism
D. Geology

15. Quick Check
2. ____ are the oldest living things thought to have first formed 3.5 billion years ago. A. Mammals B. Birds C. Trilobites D. Bacteria

16. Quick Check
3. ____ is the era dominated by life in the oceans. A. Precambrian B. Paleozoic C. Mesozoic D. Cenozoic

17. Quick Check
4. At the end of the ____ era, an asteroid hit the Earth causing mass extinction and the end of the dinosaurs. A. Precambrian B. Paleozoic C. Mesozoic D. Cenozoic

18. Quick Check
5. Which picture shows a close representation of the geologic time scale? A. B. C.
precambrian
paleozoic
mesozoic
cenozoic
paleozoic
mesozoic
cenozoic
precambrian
cenozoic
paleozoic
precambrian
mesozoic