Sunday, 28 August 2011
New claim to the earliest bacterial life
Fossils of sulphur-bacteria have been identified on ancient sand grains in 3.45 Gyr deposits in Western Australia. Hollow tubular structures clumping together and coating the grains resemble modern sulphate-reducing bacteria. Nitrogen-enriched carbonaceous walls, low in the C-13 isotope, provide chemical evidence. Also, associated pyrite crystals inferred to be the sulphurous metabolic by-product constitute circumstantial evidence. The Crawley-led team includes Oxford's Martin Brasier, who has previously cast doubt on claims of bacteria-shaped structures in the nearby 35Myr-older Apex cherts.
Claims to find earliest life evidently depend on what constitutes adequate 'evidence'. Older sedimentary rocks are more strongly metamorphosed - making for weaker evidence - yet many would support Manfred Schidlovski's older claims (~3.8 Gyr) based on C-13 isotope data, which leaves relatively little time for evolution of DNA-based life on Earth.