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

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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.