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Pilbara find points to earliest life
The evolution of oxygen-producing organisms has been pushed back another 270 million years through the discovery of new evidence in Western Australia's Pilbara region.

The discovery is the most convincing evidence yet for the point at which the Earth's current oxygenated atmosphere began to form, described as one of the defining moments in the Earth's history.

David Flannery, who presented his discovery today at the Fifth International Archean Symposium in Perth, Western Australia, argues the find is the earliest convincing sign of early oxygenic photosynthesis yet found.

Flannery, a doctoral student at the University of New South Wales Australian Centre for Astrobiology, says signs of the presence of oxygen-producing organisms were found in the rock formation known as the Tumbiana, which stretches for about 680 kilometres along the southern margin of the Pilbara crater in Western Australia.

He says the evidence, which includes stromatolites, microbially induced sedimentary structures and biomarkers - the remains of molecules synthesised by oxygen-producing cyanobacteria, are well preserved in the formation.

Cyanobacteria, commonly known as blue-green algae, are single-cell life forms that can photosynthesise oxygen.

"There is a debate in the literature as to when the first oxygen-producing organisms evolved," he says, adding that the accepted evidence is that this happened about 2.5 billion years ago.

It is generally accepted that the atmosphere became oxygenated about 2.45 billion years ago, says Flannery.

"But there are some who see evidence for cyanobacteria up to a billion years earlier than that."
First signs of oxygen

The work of Flannery and his colleagues suggests the presence of oxygen-producing cyanobacteria on the Earth at 2.72 billion years ago, some 270 million years before the atmosphere is thought to have become oxygenated.

He says the finding has implications not only for how long it took the Earth's atmosphere to become oxygenated, but may also help in the hunt for life on other planets

Flannery says solving the mystery of the oxygenation of the atmosphere may in the future help exoplanet hunters better target their search for planets able to support life.

"If for example, we find it took a billion years for the atmosphere to oxygenate, we might then target our searches for atmospheric oxygen to planets orbiting stars more than a billion years old," he says.

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