Carbonate-Associated Phosphate (CAP) Indicates Elevated Phosphate Availability in Neoarchean Shallow Marine Environments

Phosphorus is essential for cell biology, yet scarce in modern marine environments wherein free phosphate is consumed by life or titrated by calcium to form apatite minerals. The environmental conditions under which the early biosphere emerged and phosphorus was integrated throughout biochemistry is yet unknown. We measured the phosphate concentrations of 2.8–2.5 Ga shallow marine carbonate facies across six Neoarchean shelf-ramp environments. We found that the P/Ca ratios of Neoarchean stromatolites, micrites, and crystal fans were >4-fold to 12-fold more enriched in carbonate-associated phosphate than modern marine coral skeletons and abiotic Phanerozoic carbonates. Our results support the view that Archean productivity was limited by the availability of electrons rather than phosphate or other nutrients, and help explain why phosphorus is so central to the molecules, metabolisms, and bioenergetics observed in cells.