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.