Evolution- Change in life forms over time

Why do things change?

How do they change?

Estimated age of earth-4.6 Billion years

4 geologic eras

1. Precambrian

2. Paleozoic

3. Mesozoic

4. Cenozoic

episodes of mass extinction separates eras

• 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

• The history of earth is written in the rocks.

• Fossil: evidence of existence preserved in rock

• Structure indicates function

Oldest fossils found are 3.5 billion years old and are microscopic photosynthetic bacteria

Analyzing the fossil record

• Life was incredible diverse– Size, structure, function

• Episodes of mass extinction

• Episodes of evolutionary explosions

Fossil Formation

• Organism dies• Covered with mud,

sand- no decay

Compression over time = sedimentary rock and fossil

Where might fossils be forming today?

• Formation of fossils

• Casts- minerals fill in

• Mold- leaves an empty space

• Amber-preserved or frozen

• Trace or carbon imprint

Determining the age of a fossil: 2 ways

1. Relative dating

2. Absolute dating

2. Absolute dating

• More accurate than relative dating

• Uses radioactive decay of isotopes

• Isotopes are radioactive natural variations of elements

Examples of Isotopes T1/2 in years

• C-14 decays to N14 5730 years

• Uranium 235 to Lead 207 700 million

• Potassium 40 to Argon 40 1.3 billion

• Half life is the time it takes for half (50%) of the isotope to change into new form.

• “Parent” compound is C14

• “Daughter “ compound is N14

• T1/2 is 5730 years

• Start with 12.5g of C14 and 187.5 g of N14. How old is your fossil?

• Carbon 14 is used for fossils < 50,000 years old

• Potassium-40 for older specimens