1. Evolution- Change in life forms over time
Why do things change?
How do they change?

2. Estimated age of earth-4.6 Billion years
4 geologic eras
Precambrian
Paleozoic
Mesozoic
Cenozoic
episodes of mass extinction separates eras

3. At the beginning
Hot, lots of volcanic activity, no free oxygen, but lots of water vapor.
3.9 Billion years ago, oceans formed
3.5 BYA first fossil evidence of life- photosynthetic bacteria

4. The history of earth is written in the rocks.
Fossil: evidence of existence preserved in rock
Structure indicates function
2 questions – how are fossils formed and how to we determine their age
Oldest fossils found are 3.5 billion years old and are microscopic photosynthetic bacteria

5. Analyzing the fossil record
Life was incredible diverse
Size, structure, function
Episodes of mass extinction
Episodes of evolutionary explosions

6. Covered with mud, sand- no decay
Fossil Formation
Organism dies
Covered with mud, sand- no decay
Compression over time = sedimentary rock and fossil
Where might fossils be forming today?

7. Formation of fossils
Casts- minerals fill in
Mold- leaves an empty space
Amber-preserved or frozen
Trace or carbon imprint

8. Determining the age of a fossil: 2 ways
Relative dating
Absolute dating

9. Relative dating
Fossils in deepest layer are oldest

10. 2. Absolute dating
More accurate than relative dating
Uses radioactive decay of isotopes
Isotopes are radioactive natural variations of elements

11. Examples of Isotopes T1/2 in years
C-14 decays to N years
Uranium 235 to Lead million
Potassium 40 to Argon billion
Half life is the time it takes for half (50%) of the isotope to change into new form.

12. “Parent” compound is C14
“Daughter “ compound is N14
T1/2 is 5730 years
Start with 12.5g of C14 and g of N14. How old is your fossil?

13. Carbon 14 is used for fossils < 50,000 years old
Potassium-40 for older specimens