Experimental simulation of atmosphere-seawater relations in the Archaean eon of Earth's history

大气和海水的组成只能从沉积物及其化石清单中重建。对于显生界的亿万年来说，这似乎很简单，因为存在着广泛的气候敏感指标。对于早期的地球来说，环境重建更成问题。未变质的太古宙沉积物很少见，许多太古代和早元古代的沉积物没有实际的等价物。在这个项目中，介绍了允许氧化和还原的H-C-N-O大气与海水反应的实验技术。其目的是限制太古宙所允许的大气-海水组合。关键相是氢氧化铁和碳酸盐Fe2+相，它们可能是带状铁建造(BIF)中常见矿物的前驱物质。这些相的热力学稳定性可能会对海水的Fe2+(Aq)浓度、pH范围和碳酸盐碱度，以及与表层海水平衡的大气成分的pCO2和pO2范围施加较窄的限制。这一结果可能有助于更好地理解BIF是常见海洋沉积物时的太古代环境条件，并对地球历史上过去几个纪元的大气成分施加限制。

Atmospheric and seawater compositions can only be reconstructed from sediments and their fossil inventory. For the Phanerozoic eon, this seems straightforward because a wide range of climate-sensitive proxies exists. For the early Earth, environmental reconstructions are more problematic. Unmetamorphosed Archaean sediments are rare, and many sediments from the Archaean and early Proterozoic eons do not have actualistic equivalents. In this project, experimental techniques are introduced that allow to react oxidized and reduced H-C-N-O atmospheres with seawater. The aim is to constrain the atmosphere-seawater combinations permissible for the Archaean eon. Key phases are iron hydroxides and Fe2+ carbonate phases that may be precursors to common minerals in banded iron formations (BIF). The thermodynamic stabilities of these phases may place narrow limits on the Fe2+ (aq) concentrations, the pH ranges, and the carbonate alkalinities of the seawater, as well as on the pCO2 and pO2 ranges of the atmospheric compositions in equilibrium with surface seawater. The results may contribute to a better understanding of the Archaean environmental conditions when BIF were common marine sediments, as well as place constraints on the atmospheric compositions of past epochs of the Earth's history.