Problem : List all of the mass extinctions and when the occurred.

The first mass extinction occurred in the Ordovician period, about 500mya. The second occurred in the late Devonian period, about 360 mya.

Problem : List all of the mass extinctions and when the occurred.

The first mass extinction occurred in the Ordovician period, about 500mya. The second occurred in the late Devonian period, about 360 mya.

Problem : What were the earliest forms of life and how long did they exist alone on earth?

The earliest forms of life were single-celled prokaryotes. They first appear in the fossil record around 3500 mya. The next form of life, the eukaryotes, did not appear until about 1900 mya. According to this evidence, prokaryotes were the only form of life for 1600 million years.

Problem : What forms of life were among the first to colonize the land and when did this occur?

Early forms of life that colonized the land included early plants and insects. This colonization began after the Ordovician extinction.
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