Nordcee and Institute of Biology, University of Southern Denmark, 5230 Odense, Denmark;
Danish Institute of Advanced Study, 5230 Odense, Denmark.
Proc Natl Acad Sci U S A. 2021 Jun 8;118(23). doi: 10.1073/pnas.2101544118.
Oxygen concentration defines the chemical structure of Earth's ecosystems while it also fuels the metabolism of aerobic organisms. As different aerobes have different oxygen requirements, the evolution of oxygen levels through time has likely impacted both environmental chemistry and the history of life. Understanding the relationship between atmospheric oxygen levels, the chemical environment, and life, however, is hampered by uncertainties in the history of oxygen levels. We report over 5,700 Raman analyses of organic matter from nine geological formations spanning in time from 742 to 1,729 Ma. We find that organic matter was effectively oxidized during weathering and little was recycled into marine sediments. Indeed, during this time interval, organic matter was as efficiently oxidized during weathering as it is now. From these observations, we constrain minimum atmospheric oxygen levels to between 2 to 24% of present levels from the late Paleoproterozoic Era into the Neoproterozoic Era. Indeed, our results reveal that eukaryote evolution, including early animal evolution, was not likely hindered by oxygen through this time interval. Our results also show that due to efficient organic recycling during weathering, carbon cycle dynamics can be assessed directly from the sediment carbon record.
氧气浓度决定了地球生态系统的化学结构，同时也为需氧生物的新陈代谢提供燃料。由于不同的需氧生物有不同的氧气需求，因此氧气水平随时间的演变可能同时影响环境化学和生命历史。然而，大气氧气水平、化学环境和生命之间的关系，受到氧气水平历史不确定性的阻碍。我们报告了来自九个地质地层的超过 5700 次有机物质的拉曼分析，这些地层的时间跨度从 7.42 亿年到 17.29 亿年。我们发现，有机物质在风化过程中被有效地氧化，很少被再循环到海洋沉积物中。事实上，在这段时间间隔内，有机物质在风化过程中的氧化效率与现在一样高。根据这些观察结果，我们将晚古生代到新元古代大气氧气水平的最低限制在目前水平的 2%到 24%之间。事实上，我们的结果表明，真核生物进化，包括早期动物进化，在这段时间内不太可能受到氧气的限制。我们的结果还表明，由于风化过程中有机物质的有效再循环，碳循环动力学可以直接从沉积物碳记录中评估。
