Atmospheric oxygenation three billion years ago
Atmospheric oxygenation three billion years ago
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DOI：
10.1038/nature12426
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发表时间：
2013-09-26
期刊：
影响因子：
64.8
通讯作者：
Canfield, Donald E.
中科院分区：
文献类型：
--
作者：
Crowe, Sean A.;Dossing, Lasse N.;Canfield, Donald E.
人们普遍认为，在地球历史的头20亿年里，大气中的氧气浓度一直很低（低于目前水平的10（-5）倍）。大气的第一次长期氧化被认为发生在大约2,3亿年前的大氧化事件期间（2，3）。然而，地球化学的迹象表明，短暂的大气氧化可以追溯到26 - 27亿年前（4-6）。在这里，我们研究铬同位素和氧化还原敏感金属的分布在约30亿年的Nsuze古土壤和近同期Ijzermyn铁形成的Pongola超群，南非。我们发现广泛的动员氧化还原敏感性元素通过氧化风化。此外，使用我们的数据，我们计算出一个最好的最小估计大气中的氧气浓度在当时的331024倍，目前的水平。总的来说，我们的研究结果表明，大约30亿年前，大气中的氧气水平相当可观，比大氧化事件早6亿多年，比以前地球表面氧化的迹象早3亿至4亿年。
It is widely assumed that atmospheric oxygen concentrations remained persistently low (less than 10(-5) times present levels) for about the first 2 billion years of Earth's history(1). The first long-term oxygenation of the atmosphere is thought to have taken place around 2.3 billion years ago, during the Great Oxidation Event(2,3). Geochemical indications of transient atmospheric oxygenation, however, date back to 2.6-2.7 billion years ago(4-6). Here we examine the distribution of chromium isotopes and redox-sensitive metals in the approximately 3-billion-year-old Nsuze palaeosol and in the near-contemporaneous Ijzermyn iron formation from the Pongola Supergroup, South Africa. We find extensive mobilization of redox-sensitive elements through oxidative weathering. Furthermore, using our data we compute a best minimum estimate for atmospheric oxygen concentrations at that time of 331024 times present levels. Overall, our findings suggest that there were appreciable levels of atmospheric oxygen about 3 billion years ago, more than 600 million years before the Great Oxidation Event and some 300-400 million years earlier than previous indications for Earth surface oxygenation.