A microbial bacterial fossil find is being hailed as proof that life existed in the oxygen-free environment of Earth, 3.4 billion years ago.
The Strelley Pool Formation in Western Australia was once a beach, but is now more than 100 Km inland near(ish) the town of Marble Bar, and is popular among paleontologists because of the stromatolites preserved there.
According to a report in Nature, the structures spotted in black sandstone at the Strelley Pool appear to have biological origins. The researchers, led by University of Oxford paleobiologist Professor Martin Brasier, said the 5-80 micrometer structures show traces of cell walls and spherical, rod and ellipsoid shapes.
However, the report notes that paleontogists have been disappointed in the past. Since microbes lack skeletons to leave conveniently large and unmistakable fossils, their presence in ancient Earth has to be inferred by analysis of rocks’ microscopic structures and chemical composition.
The uniformity of the structures believed to be cell walls lends credence to the idea that the newly-found structures are biological rather than mineral in origin, as does the depletion of Carbon-12 in the surrounding rocks. The researchers also note that the distribution of iron sulphide around the fossils’ cell walls seems to reflect the pattern of pyrites distribution around modern bacteria.
If the Strelley Pool structures are fossils of microbes, they will have been surviving in an atmosphere quite different to the one we know now, and will have metabolized sulphur rather than oxygen for energy.
According to Professor Brasier’s colleague Dr David Wacey of the University of Western Australia, the find pushes the fossil record of life 200 million years. Their ability to survive in a zero-oxygen environment has also added to speculation that life could have once existed on an ancient Mars. ®
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