The world's oldest rock found in Australia is giving up its secrets

The oldest rock samples, from 3.2 billion years ago, were collected in the desert in northwestern Australia. Image: R. Buick / University of Washington

Science has found strong indications that life existed on earth a billion years more in time than previously thought, according to a study of the world’s oldest rock found in Western Australia.

The ability to use atmospheric nitrogen to support more widespread life was thought to have appeared roughly 2 billion years ago.

But research from the University of Washington, looking at some of the planet’s oldest rocks, has found evidence that 3.2 billion years ago life was already pulling nitrogen out of the air and converting it into a form which could support larger communities.

“People always had the idea that the really ancient biosphere was just tenuously clinging on to this inhospitable planet, and it wasn’t until the emergence of nitrogen fixation that suddenly the biosphere become large and robust and diverse,” says Roger Buick, a professor of Earth and space sciences.

“Our work shows that there was no nitrogen crisis on the early Earth, and therefore it could have supported a fairly large and diverse biosphere.”

The results are published in the journal Nature.

The authors analysed 52 rock samples ranging in age from 2.75 to 3.2 billion years old, collected in South Africa and northwestern Australia.

These are some of the oldest and best-preserved rocks on the planet. They also formed before the atmosphere gained oxygen, roughly 2.3 to 2.4 billion years ago, and so preserve chemical clues which have disappeared in modern rocks.

Even the oldest samples, 3.2 billion years old – three-quarters of the way back to the start of the planet – showed chemical evidence that life was pulling nitrogen out of the air.

The authors say that this may be further evidence that some early life may have existed in single-celled layers on land, exhaling small amounts of oxygen.

“We’ll never find any direct evidence of land scum one cell thick, but this might be giving us indirect evidence that the land was inhabited,” Buick said.

“Microbes could have crawled out of the ocean and lived in a slime layer on the rocks on land, even before 3.2 billion years ago.”

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