Serpentinization as a route to liberating phosphorus on habitable worlds

Abstract Planetary habitability is in part governed by nutrient availability, including the availability of the element phosphorus. The nutrient phosphorus plays roles in various necessary biochemical functions, and its biogeochemical cycling has been proposed to be extremely slow due to a strong coupling to the rock cycle via mineral weathering. 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 serpentinite rocks to include the ion phosphite (HPO32- with P3+) and show that reduction of phosphate to phosphite is predicted from thermodynamic models of serpentinization. As a result, as olivine in ultramafic rocks alters to serpentine minerals, phosphorus as soluble phosphite 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.