Department of Earth and Space Sciences/Cross-Campus Astrobiology Program, University of Washington, Box 351310, Seattle, WA, 98195-1310, USA.
Geoscience Research Division, Scripps Institution of Oceanography, La Jolla, CA, 92093, USA.
Nat Commun. 2020 Jun 2;11(1):2774. doi: 10.1038/s41467-020-16493-1.
Aerobic lifeforms, including humans, thrive because of abundant atmospheric O, but for much of Earth history O levels were low. Even after evidence for oxygenic photosynthesis appeared, the atmosphere remained anoxic for hundreds of millions of years until the ~2.4 Ga Great Oxidation Event. The delay of atmospheric oxygenation and its timing remain poorly understood. Two recent studies reveal that the mantle gradually oxidized from the Archean onwards, leading to speculation that such oxidation enabled atmospheric oxygenation. But whether this mechanism works has not been quantitatively examined. Here, we show that these data imply that reducing Archean volcanic gases could have prevented atmospheric O from accumulating until ~2.5 Ga with ≥95% probability. For two decades, mantle oxidation has been dismissed as a key driver of the evolution of O and aerobic life. Our findings warrant a reconsideration for Earth and Earth-like exoplanets.
需氧生物，包括人类，之所以能够繁荣昌盛，是因为大气中富含氧气，但在地球历史的大部分时间里，氧气含量都很低。即使在产氧光合作用出现之后，大气仍然缺氧数亿年，直到约 24 亿年前的大氧化事件。大气增氧的延迟及其时间仍然知之甚少。最近的两项研究表明，地幔从太古代开始逐渐氧化，这导致人们猜测这种氧化作用使大气增氧成为可能。但这种机制是否有效尚未经过定量检验。在这里，我们表明，这些数据表明，太古宙火山气体的还原性可能使大气中的氧气无法积累，直到约 25 亿年前，其概率≥95%。二十年来，地幔氧化一直被认为不是氧气和有氧生命演化的关键驱动因素。我们的发现值得重新考虑地球和类地系外行星。
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