Identifying traces of life in very ancient rocks is understandably difficult, and more than one claim for the oldest evidence of life later has not withstood scrutiny after making its initial splash in the headlines or even after being incorporated into textbooks. Tiny structures initially identified as microfossils have been reinterpreted to be the result of inorganic rather than organic processes.
A recent discovery, however, offers convincing evidence for the presence of relatively large, organic-walled microfossils in rocks 3.2 billion years old from South Africa. The structures are interpreted as organic on the basis of their cell-like morphology and ultrastructure, the fact that they occur in large numbers, as would microfossils, and their presence in rocks that represent environments that would have been amenable to living organisms. Time will tell.
Source and photo credit: Javaux, E.J., et al., 2010. Organic-walled microfossils in 3.2-billion-year-old shallow-marine silicilastic deposits. Nature 463:934-938.
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