Biospheric oxygenation and atmospheric evolution across Earth's earliest glacial episodes

地球上最早的冰川形成的原因(S)尚不清楚，但太阳光度和温室气体(主要是甲烷和二氧化碳)丰度变化的模型表明，大气氧化状态的变化可能驱动了早期古元古代(约2.2至2.4Ga)冰期的振荡循环。海洋和大气的氧化还原状态反映在保存在古代沉积物中的硫酸盐和硫化物矿物的多种硫同位素数据(32S、33S、34S和36S)中。在最新的太古宙沉积物中发现了与质量无关的硫同位素分馏，表明大气氧低于10-5PAL。然而，到南非最早的古元古代冰期时，硫同位素记录表明，pO2显著上升，可能达到几个百分点或更高。这项研究提议通过对南非下一个最年轻的冰期的高分辨率研究，在深部钻探岩芯中通过大约2.3Ga Timeball Hill组进行研究，其中包括对微小的硫同位素变化--包括有机结合硫--的研究，这种变化在以前的任何次要同位素研究中都没有被研究过。结果应该提供经验约束，即大气氧化还原状态的变化推动了最早的冰川周期。

The cause(s) of Earth s earliest glaciations are poorly understood, but models that relate changes in solar luminosity and greenhouse gas abundance (primarily methane and carbon dioxide) suggest that variations in the oxidation state of the atmosphere may have driven the oscillatory cycle of early Paleoproterozoic (ca. 2.2 to 2.4 Ga) ice ages. The redox state of the oceans and atmosphere is reflected in multiple sulphur isotope data (32S, 33S, 34S, and 36S) of sulphate and sulphide minerals preserved in ancient sediments. In the latest Archean sediments reveal mass-independent sulphur isotope fractionation, suggesting that atmospheric oxygen was less than 10-5 PAL. However, by the time of the earliest Paleoproterozoic ice age in South Africa, the sulphur isotopic record suggests a significant rise in pO2, to perhaps a few percent or higher. This study proposes to investigate the run up to the next youngest ice age in South Africa, through a high resolution study of minor sulphur isotope variations - including organic-bound sulphur, a proxy that has not yet been investigated in any previous minor isotope study - in deep time drill cores through the ca. 2.3 Ga Timeball Hill Formation, which lies immediately beneath a widespread glacial diamictite. Results should provide empirical constraints that changes in the atmospheric redox state drove the earliest glacial cycles.