Serpentinizing systems -- in which aqueous alteration of ultramafic rocks yields highly reducing and alkaline fluids -- have been suggested as possible niches for photosynthesis-independent ecosystems on Earth and beyond. To date, most research has focused on systems characterized by extremes of pH or redox potential, and on surface expressions (e.g., springs or vents) where deeply-sourced fluids mix with the surface chemistry.
To capture a broader cross-section of the geochemical diversity in serpentinizing systems, and to assess the biological potential of unmixed subsurface fluids, we established the Coast Range Ophiolite Microbial Observatory, a series of wells drilled into the actively serpentinzing subsurface of the McLaughlin Natural Reserve (Lake County, California).
Observations of mineralogy and microbial community composition in cored materials, aqueous geochemistry in recovered well fluids, and biological process rates in fluids and cored materials were combined with geochemical and bioenergetic models that relate host-rock composition and hydrology to biological potential. Both modeled and observational results indicate that natural variability in serpentinizing systems can generate a broad spectrum of geochemical conditions, and correspondingly wide range of biological potential. This range of conditions appears to cross the boundary from habitable to uninhabitable with regard to biological energy requirements, tolerance to extremely alkaline pH, or both.