Zinc enrichment and isotopic fractionation in a marine habitat of the c. 2.1 Ga Francevillian Group: A signature of zinc utilization by eukaryotes?

Constraining the timing of eukaryogenesis and divergence eukaryotic clades is a major challenge in evolutionary biology. Here, we present trace metal concentration zinc isotope data for c. 2.1 billion-year-old Francevillian Group pyritized structures, previously described as putative remnants first colonial multicellular organisms, their host black shales. Relative to rocks, structures are strongly enriched zinc, cobalt nickel, by at least one order magnitude, with markedly lighter compositions. A metabolic demand high concentrations aqueous cobalt, nickel combined preferential uptake isotopes may indicate metalloenzyme utilization eukaryotes marine habitats billion years ago. Once confirmed, this would provide critical calibration point eukaryogenesis, suggesting that innovation have happened contemporaneously elevated atmospheric oxygen levels during latter part Great Oxidation Event, some 400 million earlier than currently widely accepted.