Traces of Early Life

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Science  29 Jan 1999:
Vol. 283, Issue 5402, pp. 601f
DOI: 10.1126/science.283.5402.601f

Most of Earth's oldest sedimentary rocks are metamorphosed, which has made it difficult to identify early fossils or determine when life on Earth began. The oldest fossils that have been found date to about 3500 million years ago. One common signature of life is the presence of carbon with a low carbon-13/carbon-12 ratio. Rosing (p. 674) reports such low ratios for graphite layers and globules in metamorphosed sedimentary rocks dated at about 3700 million years ago in Greenland.

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