Serpentinization as a route to liberating phosphorus on habitable worlds

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. (C) 2022 Elsevier Ltd. All rights reserved.

Automated summary

Phosphorus is not limited to existing solely as phosphate, but can also exist as phosphite in extremely reducing environments. By studying the speciation of phosphorus in serpentinite rocks and muds, researchers have found that phosphate can be reduced to phosphite. The study suggests that under low redox conditions, this transformation may release more phosphite, providing a key nutrient for life.