Evolution- Change in life forms over time Why do things change? How do they change?
Mar 27, 2015
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