Biological Processes Related to Serpentinization: Expected vs Observed Patterns

Abstract:

Serpentinization is a water-rock reaction that drives the evolution of micro- to mega-scale habitability in ultramafic rocks, through the aqueous alteration of olivine and pyroxene in parent rocks, and the production of H₂, CH₄, and (possibly) biologically useful organic compounds. This process may pervade extensive areas of silicate planetary bodies, in geologic settings as diverse as cratered fracture zones and fault systems in ultramafic rocks, hydrothermal flow systems operating near crust/mantle interfaces, and deep subsurface groundwater flow systems. Serpentinization causes transformations in mineralogy, rock geochemistry, and co-occurring associated water chemistry that together control the feasibilities of prominent microbial metabolisms. Changing activities of aqueous H₂, CH₄, CO₂, CO, organic acids, H⁺, and other redox-sensitive dissolved species shift the metabolic landscape in serpentinites in predictable ways, providing expected patterns in community metabolic strategies. I discuss emerging patterns in observations from terrestrial sites of serpentinization, marine and continent-hosted, and consider how they may allow testing of some pertinent hypotheses in geomicrobiology in terrestrial and extraterrestrial settings.