1. Geologic Time

2. A. Earth ≈ 4.6 Billion Years Old

3. Billion = 4,600,000,000

5. 2. Most Geologic Time is divided into eras and periods

6. B. Precambrian Time = 88% of Earth’s History

7. 1. Precambrian Earth: lava flowed over the surface – building the continents

8. 2. First Life. Bacteria found in rocks from 3
2. First Life? Bacteria found in rocks from 3.5 Billion Years Ago (BYA)

9. 3. About 2.5 BYA, bacteria started using sunlight to make their own food.

13. C. The Paleozoic Era
1. began ~544 Million Years
Ago (MYA)

14. 2. Most Paleozoic animals were invertebrates

15. Cambrian Species

17. 3. After ~300 million years, about 95% of Earth’s species DIE due to…

18. DRASTIC climate change caused by Pangaea forming (about 260 MYA)

19. D. The Mesozoic Era
1. began ~245 MYA

20. 2. Mesozoic = Age of Dinosaurs (or Reptiles)

21. Mesozoic Era

23. 3. Dinosaurs ruled the Mesozoic, but the first mammals also appeared in that era.

24. 4. Dinosaurs lived from ~225 MYA to ~65 MYA

25. 5. About 180 million years after the start of the Mesozoic era, a massive impact filled the sky with debris and changed the climate

27. E. The Cenozoic Era 1. began ~65 MYA and continues today.

28. 2. Cenozoic = Age of Mammals

30. 3. Last Ice Age was ~10,000 years ago