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Pushing back an oxygen-rich atmosphere

Hematite crystals in Australian rocks hint that photosynthesizing life may have existed earlier than previously thought

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2:16pm, March 15, 2009

Tiny crystals of iron oxide in ancient Australian rocks offer evidence that the Earth’s atmosphere held significant amounts of oxygen far earlier than previously thought, a new study suggests.

Large quantities of oxide minerals in rocks around the world indicate that the atmosphere had at least small amounts of oxygen by 2.2 billion years ago (SN: 1/24/04, p. 61). And the presence of certain biomarkers in Australian rocks has been hailed as evidence that oxygen-making organisms had evolved by 2.7 billion years ago, but recent studies have cast some doubt on that earlier date (SN: 11/22/08, p. 5).

Now, analyses of rocks laid down 3.46 billion years ago in what is now Australia push back the oxygen era even further, Hiroshi Ohmoto, a geochemist at Pennsylvania State University in University Park, and his colleagues contend online March 15 in

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