Meteoritic and hydrothermal sources of reduced phosphorus in the early Archean

Reduced phosphorus (P), in particular phosphite [P(III)] has been identified as a potentially key ingredient for prebiotic chemistry that may have facilitated the phosphorylation of organic compounds. One possible source of reduced P is asteroid impacts. To test this hypothesis, we investigated P redox speciation across an impact deposit that formed at 3.26 Ga in the Barberton Greenstone Belt in South Africa and that has previously been linked to extraterrestrial delivery of phosphate [P(V)]. Our results show that at least 0.1% of the total P that was delivered by the impactor was indeed in reduced form. In addition, we found a persistent background of 10−200 ppb P(III) in all samples, independent from the impact layer. This background may be explained by post-depositional silicifying fluids that mobilized P(III) from underlying oceanic crust. We conclude that asteroid impacts and hydrothermal fluids could have provided reduced P to the early oceans and supported the origin and early evolution of life.