The first known fossils of living cells were preserved in rocks that are 3.5 billion years old, but scientists postulated that the first cells arose many millions of years prior to this time. These first cells were most likely ...

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The first cells were most likely anaerobic, heterotrophic, prokaryotic because the early Earth's atmosphere lacked oxygen, and these simple cells would have relied on the organic molecules in their environment for energy, without the complex organelles found in eukaryotes.

The First Known Fossils of Living Cells Were Preserved in Rocks