2. Summary of Major Events in the Evolution of Life

3. 18 Billion Years Ago b BIG BANG b The universe began with the so called Big Bang, an event about 13 - 18 billion years ago, during which all the matter in the universe was scattered in enormous explosion.

4. 4.6 Billion Years Ago  Big Rock: Earth Forms b The first atmosphere began to form from: CO2, CO, water vapor, N2, H2S, and small traces of CH4, and NH3.  Lack of Oxygen.

5. 3.8 Billion Years Ago b THE ORIGIN OF LIFE. b First Prokaryotic Cells Appear.

6. 3.2 Billion Years Ago b Autotrophs. b Little change in atmosphere.

7. 2.8 Billion Years Ago b Strong evidence of photosynthetic organisms. b Oxygen is given off into atmosphere, but still is less than 1%.

8. 2.0 Billion Years Ago b Blue-Green Algae. b Ozone screen begins to form.

9. 1.5 Billion Years Ago b First eukaryotic cells appear. b 2% oxygen in atmosphere.

11. 670 Million Years Ago b Multicellular organisms. b 7% oxygen in atmosphere.

12. 550 Million Years Ago b Shelled Animals. b Early Land Plants. b 10 % Oxygen in Atmosphere.

13. 500 Million Years ago b Fishes. b Land plants. b Atmosphere same as today, 20% oxygen. b Complete ozone screen.

14. 395 Million Years Ago b First amphibians.

15. 321 Million Years Ago b First reptiles.

16. 225 million years Ago b First flowering plants. b First birds and mammals.

17. Mammals

18. 1 - 2 Million Years Ago b Human Kind - Homo sapiens.