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Nat Commun. 2015 Dec 18;6:10157. doi: 10.1038/ncomms10157.

Selenium isotope evidence for progressive oxidation of the Neoproterozoic biosphere.

Author information

Institute of Earth and Planetary Sciences, University College London and Birkbeck, University of London, Gower Street, London WC1E 6BT, UK.
Bristol Isotope Group, School of Earth Sciences, Bristol University, Wills Memorial Building, Queen's Road, Bristol BS8 1RJ, UK.
Department of Earth and Space Sciences, University of Washington, Seattle, Washington 98195, USA.
School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK.
Department of Geology, Utah State University, Logan, Utah 84322, USA.
NordCEE, University of Southern Denmark, 5230 Odense M, Denmark.


Neoproterozoic (1,000-542 Myr ago) Earth experienced profound environmental change, including 'snowball' glaciations, oxygenation and the appearance of animals. However, an integrated understanding of these events remains elusive, partly because proxies that track subtle oceanic or atmospheric redox trends are lacking. Here we utilize selenium (Se) isotopes as a tracer of Earth redox conditions. We find temporal trends towards lower δ(82/76)Se values in shales before and after all Neoproterozoic glaciations, which we interpret as incomplete reduction of Se oxyanions. Trends suggest that deep-ocean Se oxyanion concentrations increased because of progressive atmospheric and deep-ocean oxidation. Immediately after the Marinoan glaciation, higher δ(82/76)Se values superpose the general decline. This may indicate less oxic conditions with lower availability of oxyanions or increased bioproductivity along continental margins that captured heavy seawater δ(82/76)Se into buried organics. Overall, increased ocean oxidation and atmospheric O2 extended over at least 100 million years, setting the stage for early animal evolution.

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