Ch. 6.1 Earth has been home to living things for about 3.8 billion

Vocabulary: fossil, mass extinction, multicellular organism, unicellular organism

Review
1. Fossils show signs of life as it existed millions of years ago.
2. Unicellular organisms contributed to Earth´s atmosphere, which did not always contain the oxygen it does now.
3. Extinction occurs when the last member of a species dies. Permian Extinction- 90% of ocean life became extinct; Cretaceous Extinction-the dinosaurs died.
4. Absolute dating tells when fossils were formed. Relative dating compares the ages of fossils. Absolute dating cannot be used on all fossils, so the two methods combined give an accurate picture.
5. Student´s timelines should show the progression of life on Earth- unicellular organisms, multicellular organisms, life inthe oceans, and the moving to land.

Fossils

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