Fossil dates Earth's first breath
Australian scientists have found evidence of bacteria that proves aerobic life began on Earth 2.5 billion years ago.
This week in Nature Roger Summons from the Australian Geological Survey Organisation (AGSO) in Canberra, reports the discovery of oxygen-creating cyanobacteria in 2.5 billion year old shale from Mount McRae in Western Australia. The discovery is the earliest evidence yet for the point at which the Earth's current atmosphere began to form, described as one of the defining moments in the Earth's history.
"The previous estimation of this moment was closer to 3.5 billion years," according to Graham Logan from AGSO. "But, the evidence for this age could only be inferred and is very equivocal".
The AGSO group have now developed a diagnostic tool that they say provides the first real evidence of the presence of cyanobacteria and therefore oxygen in the atmosphere.
The group was able to isolate a signature molecule from living cyanobacteria then went looking for it in the ancient rock.
"Now we have a molecule that proves the existence of cyanobacteria but we have proved only that this chemical change in the atmosphere started at least 2.5 billion years ago," said Logan.
The fossils are actually organic compounds that, despite the ravages of time, still bear a close resemblance to the compounds left behind by the cyanobacteria when they were living. Summons' group show that an unmistakable 'biomarker' of cyanobacteria, 2-methylhopane, is abundant in organic-rich sediments as old as 2.5 billion years.