美国犹他大学Ostrander, Chadlin M.团队最新的研究报道了23亿年前大气—海洋氧化作用耦合的开始。2024年6月12日出版的《自然》杂志发表了这项成果。

据悉，25亿年前在太古代—元古代过渡后不久，分子氧(O₂)的初始上升比曾经设想的单一阶段变化更为复杂。与硫质量无关的分馏法记录表明，大气中O₂是振荡上升的，直到大约22亿年前曾多次回到缺氧状态。然而，对同期海洋氧化动力学的限制很少，妨碍人们了对行星氧化作用的整体理解。

本文报道了来自南非Transvaal超群海相页岩的铊(Tl)同位素比值和氧化还原敏感元素数据。研究发现，与相同页岩中大气氧化作用的硫同位素证据同步，较低的自生²⁰⁵Tl/²⁰³Tl比值表明，含氧海底广泛存在氧化锰埋藏，较高的氧化还原敏感元素丰度与膨胀的含氧水域一致。

当硫同位素数据显示短暂恢复到缺氧大气状态时，这两个特征就消失了。研究数据将最近确定的早期地球大气O₂动态与海洋领域联系起来，标志着地球氧化还原历史上远离异质性和高度本地化的“绿洲”式氧化的一个重要转折点。

附：英文原文

Title: Onset of coupled atmosphere–ocean oxygenation 2.3 billion years ago

Author: Ostrander, Chadlin M., Heard, Andy W., Shu, Yunchao, Bekker, Andrey, Poulton, Simon W., Olesen, Kasper P., Nielsen, Sune G.

Issue&Volume: 2024-06-12

Abstract: The initial rise of molecular oxygen (O₂) shortly after the Archaean–Proterozoic transition 2.5 billion years ago was more complex than the single step-change once envisioned. Sulfur mass-independent fractionation records suggest that the rise of atmospheric O₂ was oscillatory, with multiple returns to an anoxic state until perhaps 2.2 billion years ago. Yet few constraints exist for contemporaneous marine oxygenation dynamics, precluding a holistic understanding of planetary oxygenation. Here we report thallium (Tl) isotope ratio and redox-sensitive element data for marine shales from the Transvaal Supergroup, South Africa. Synchronous with sulfur isotope evidence of atmospheric oxygenation in the same shales, we found lower authigenic ²⁰⁵Tl/²⁰³Tl ratios indicative of widespread manganese oxide burial on an oxygenated seafloor and higher redox-sensitive element abundances consistent with expanded oxygenated waters. Both signatures disappear when the sulfur isotope data indicate a brief return to an anoxic atmospheric state. Our data connect recently identified atmospheric O₂ dynamics on early Earth with the marine realm, marking an important turning point in Earth’s redox history away from heterogeneous and highly localized ‘oasis’-style oxygenation.

DOI: 10.1038/s41586-024-07551-5

Source: https://www.nature.com/articles/s41586-024-07551-5