SME
Historical Geology · Problem type
Which eon an event belongs to
Use this for “The Great Oxidation Event left the first red beds. In which eon did it happen?”
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In which eon did it happen?
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Oxygen, then complex cells, then animals: each eon is marked by what life could do.
Assumptions
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Archean: 4,000 to 2,500 Ma. Proterozoic: 2,500 to 539 Ma. Phanerozoic: 539 Ma to today.
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Life stayed single-celled and mostly bacterial through the Archean.
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Phanerozoic means “visible life”: it starts with the shells and skeletons of the Cambrian.
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