EARTH HISTORY

Ancient soils record early oxygen

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Science  03 Oct 2014:
Vol. 346, Issue 6205, pp. 51
DOI: 10.1126/science.346.6205.51-g

The Great Oxidation Event marks the permanent appearance of appreciable concentrations of oxygen in Earth's atmosphere 2.4 billion years ago, a consequence of biological activity. Determining the history of oxygen levels leading up to this time, however, is hindered by spotty and incomplete records. Mukhopadhyay et al. describe an ancient soil deposit in eastern India that formed 3 billion years ago, or ∼600 million years before the Great Oxidation Event. Geochemical clues in the soil and overlying sediments point to a fleeting presence of free oxygen at the time the soil formed. It is likely that several small, short-lived oxygenation events occurred before Earth's atmosphere reached high oxygen levels permanently.

Geology 10.1130/G36091.1 (2014).

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