Pogge von Strandmann Philip A E, Stüeken Eva E, Elliott Tim, Poulton Simon W, Dehler Carol M, Canfield Don E, Catling David C
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.
Nat Commun. 2015 Dec 18;6:10157. doi: 10.1038/ncomms10157.
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.
新元古代（距今10亿至5.42亿年前）的地球经历了深刻的环境变化，包括“雪球”冰川作用、氧化作用以及动物的出现。然而，对这些事件的综合理解仍然难以捉摸，部分原因是缺乏追踪海洋或大气中微妙氧化还原趋势的指标。在这里，我们利用硒（Se）同位素作为地球氧化还原条件的示踪剂。我们发现在新元古代所有冰川作用前后的页岩中，δ(82/76)Se值呈下降趋势，我们将其解释为硒氧阴离子的不完全还原。这些趋势表明，由于大气和深海的逐渐氧化，深海中硒氧阴离子的浓度增加。在马里诺冰期之后，较高的δ(82/76)Se值叠加在总体下降趋势之上。这可能表明氧含量较低，氧阴离子的可用性较低，或者大陆边缘的生物生产力增加，从而将重的海水δ(82/76)Se捕获到埋藏的有机物中。总体而言，海洋氧化和大气氧气增加至少持续了1亿年，为早期动物进化奠定了基础。
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