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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

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).

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