MINERALOGICAL UNDERPINNINGS AND PLANETARY IMPLICATIONS OF TERRESTRIAL AND MARTIAN SERPENTINIZATION

Serpentinization, the water-driven alteration of olivine-rich rocks to serpentine minerals, (hydr)oxides, and H₂, plays an integral role in solar system evolution. Minerals and H₂ generated through this reaction have been implicated in processes as wide-ranging as originating life on Earth and Mars, transporting water and oxidized Fe into Earth’s mantle, enhancing greenhouse warming early in the history of both planets, and fueling rock-based life on Earth and, perhaps, other rocky bodies throughout the solar system. Although serpentinization has been studied intensely for at least a century, recent crystallographic, thermodynamic, and kinetic insights into the mineralogical underpinnings of both terrestrial and Martian serpentinization continue to provide new, foundational insights. Specifically, chemical- and redox-specific constraints on the mechanisms of oxidized Fe incorporation into serpentine and its partitioning into magnetite are yielding fundamental insights into the generation of H₂ during the serpentinization process. Interestingly, these results show important contrasts in the mechanism of H₂ generation as a function of protolith composition: Mg-cronstedtite solid-solutions facilitated by Si deficiencies in the serpentine structure are dominant during serpentinization of the terrestrial mantle, while vacancy-enabled Mg-hisingerite solid-solutions are dominant during serpentinization of the Fe-rich rocks representative of the Martian crust and upper mantle. Thermodynamic calculations based on these fundamental observations suggest that low-temperature serpentinization in Earth’s silica-rich early oceans would have produced orders of magnitude less H₂ than their modern counterparts, whereas serpentinites on early Mars would have produced around five times more H₂. Moving forward, kinetic experiments and reactive transport simulations designed to explore coupled fluid, solute, and heat transport in serpentinizing systems are helping to predict the implications of these observations for planetary-scale processes.