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Precambrian Life

The chemical signature of life has been found in the oldest sedimentary rocks in the world, dating to 3.85 billion years ago. The oldest actual fossils of bacteria date back 3.5 billion years, about 350 million years after the earliest chemical signs of life. Eukaryotic cells -- the kind that make up the bodies of multicellular organisms -- leave a different chemical signature, which has been found in rocks as old as 2.7 billion years, 1.5 billion years before the first traditional fossils appear. (

Credits: Excerpted from Evolution: The Triumph of an Idea, by Carl Zimmer. 2001 WGBH Educational Foundation and Clear Blue Sky Productions. Reprinted with permission of HarperCollins.

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Deep Time/History of Life

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