1. Notes #6: Geologic Timescale

2. I. What was it like on early Earth ?
Very hot
Meteorites colliding into earth
Frequent volcanic activity
Atmosphere with little oxygen & lots of nitrogen & carbon dioxide

3. THEN...
Approximately 3.9 billion years ago the earth cooled & the water vapor in the atmosphere condensed - creating the earth’s oceans.

4. scientists believe the first organisms appeared.
AND
scientists believe the first organisms appeared.

5. II. What is the Geologic Time Scale ?
Calendar of Earth’s history based on evidence found in rocks.
Earth began in the Precambrian era.
We live in the Cenozoic Era.

6. III. What is the Precambrian era?
4.5 billion years ago to 550 million years ago
87% of Earth’s history
Prokaryotes begin –bacteria
Eukaryotes begin– multicellular organisms

7. Beginning of fish, plants &reptiles
IV. The Paleozoic Era?
550 to 245 million years ago
Beginning of fish, plants &reptiles
Largest mass extinction in the fossil record was at the end of this era

8. Beginning of dinosaurs, mammals, flowering plants, birds
V. The Mesozoic Era?
245 to 66 million years ago
Beginning of dinosaurs, mammals, flowering plants, birds
Mass extinction causing the dinosaurs to die at the end of this era –due to a meteor collision?

9. 66 million years ago to present day Beginning of complex mammals
VI. The Cenozoic Era?
66 million years ago to present day
Beginning of complex mammals
Humans evolve

10. Summary How old do scientists believe the earth to be?
How has life on earth changed from then to now?

11. 13. Gradualism
Organisms evolve in a process of slow and constant change

12. 14. Punctuated Equilibrium
The idea that species evolve in short bursts, and then go through long periods with little evolution.