Department of Geology and Geophysics, Yale University, New Haven, CT, USA.
Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI, USA.
Geobiology. 2019 Nov;17(6):579-593. doi: 10.1111/gbi.12360. Epub 2019 Aug 22.
Atmospheric oxygen levels control the oxidative side of key biogeochemical cycles and place limits on the development of high-energy metabolisms. Understanding Earth's oxygenation is thus critical to developing a clearer picture of Earth's long-term evolution. However, there is currently vigorous debate about even basic aspects of the timing and pattern of the rise of oxygen. Chemical weathering in the terrestrial environment occurs in contact with the atmosphere, making paleosols potentially ideal archives to track the history of atmospheric O levels. Here we present stable chromium isotope data from multiple paleosols that offer snapshots of Earth surface conditions over the last three billion years. The results indicate a secular shift in the oxidative capacity of Earth's surface in the Neoproterozoic and suggest low atmospheric oxygen levels (<1% PAL pO ) through the majority of Earth's history. The paleosol record also shows that localized Cr oxidation may have begun as early as the Archean, but efficient, modern-like transport of hexavalent Cr under an O -rich atmosphere did not become common until the Neoproterozoic.
大气氧含量控制着关键生物地球化学循环的氧化侧，并限制了高能量代谢的发展。因此，了解地球的氧化作用对于更清楚地了解地球的长期演化至关重要。然而，即使是关于氧气上升的时间和模式的基本方面，目前也存在激烈的争论。陆地环境中的化学风化作用与大气接触，使古土壤成为追踪大气 O 水平历史的潜在理想档案。在这里，我们从多个古土壤中提供了稳定的铬同位素数据，这些数据提供了过去 30 亿年来地球表面条件的快照。结果表明，地球表面的氧化能力在新元古代发生了长期变化，并表明大气氧含量较低（<1% PAL pO ）在地球历史的大部分时间里。古土壤记录还表明，局部 Cr 氧化可能早在太古代就已经开始，但只有在新元古代，富含 O 的大气下，六价 Cr 的有效、现代式运输才变得普遍。
