¹Matthew A. Pasek, ²Arthur Omran,¹Tian Feng,¹Maheen Gull,¹Carolyn Lang,¹Josh Abbatiello,¹Lyle Garong,¹Ray Johnston,¹Jeffrey Ryan,³Heather Abbott-Lyon
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.09.027]
¹School of Geosciences, University of South Florida, 4202 E Fowler Ave NES 204, Tampa, FL 33620, USA
²Department of Chemistry, University of North Florida, Jacksonville, FL 32224, USA
³Department of Chemistry, Kennesaw State University, Kennesaw, GA 30144, USA
Copyright Elsevier

A general assumption about the geochemical behavior of phosphorus (P) is that it exists exclusively in the +5 oxidation as phosphate. However, in extremely reducing environments, other oxidation states of phosphorus such as +3 may also be stable. Such environments—if prevalent globally—may determine planetary habitability, which is in part governed by nutrient availability, including the availability of the element phosphorus. Here we show a route to P liberation from water-rock reactions that are thought to be common throughout the Solar System. We report the speciation of phosphorus in several serpentinite rocks and muds to include the ion phosphite (HPO32- with P3+) and show that reduction of phosphate to phosphite may be predicted from thermodynamic models of serpentinization. Furthermore, the amount of phosphite exceeds the amounts predicted from thermodynamic models in three of nine samples analyzed. As a result, as olivine and other silicates in ultramafic rocks alter to serpentine minerals, phosphorus as the significantly more soluble and reactive phosphite ion should be released under low redox conditions, liberating this key nutrient for life. Thus, this element may be accessible to developing life where water is in direct contact with ultramafic rock, providing a source of this nutrient to potentially habitable worlds.