Tracking the co-evolution of microbial sulfur metabolisms and geodynamics at the Eoarchean - Paleoarchean (3800-3200 Ma) transition

Chemolithoautotrophy, free energy from chemical disequilibria in crustal environments, apparently sustained the last universal common ancestors (LUCAs) of all life. If the LUCAs relied on the reductive Acetyl-CoA metabolic pathway via abundant H₂ (e^- donor) and bicarbonate (e^- acceptor), they were confined to hydrogenous (H₂-producing) metalliferous (ultra-)magnesian alkaline hydrothermal (>50°C) systems. The later advent of photoautotrophy provided a new plentiful e^- donor (C_org) that allowed early life to exploit Sulfur (S) compounds as an energy source. Here, we report new multiple S-isotope (³²S, ³³S, ³⁴S; Δ³³S) data from authigenic sedimentary sulfides in Eoarchean-Paleoarchean sedimentary rocks from Isua (West Greenland) and South Africa (Barberton) to trace this early metabolic evolution. Our aim is to: (i) pinpoint in time and space when life began to influence the marine S cycle; (ii) follow changes in primary (C_org) production; (iii) model commutations to Eoarchean-Paleoarchean geodynamic regimes; and (iv) experimentally test how C_org is altered. Geodynamic scenarios particular to the Eoarchean-Paleoarchean Earth supported early biodynamic environments in both plate tectonics vs. non-plate tectonic contexts. For example, crust production modulates nutrient supply to the oceans which in turn influences the timing and tempo of metabolic innovation. Bio-geo-dynamic changes in the early Archean set the stage for the eventual emergence of the Eukaryotes.