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 Precambrian Paleozoic Mesozoic 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 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

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

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?

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 Relative dating Absolute dating

Relative dating Fossils in deepest layer are oldest

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