Lawrence Berkeley National Laboratory

Mars appears to have experienced little plate tectonic activity and compositional differentiation of primitive lithosphere. Ophiolite terranes, sections of mafic and ultramafic oceanic crust and upper mantle that have been obducted onto land, are therefore good analogs for Mars. The characteristic mineralogy, aqueous geochemistry, and microbial communities of their associated cold-water alkaline springs represent a particularly compelling analog for potential life-bearing systems. Serpentinization, the reaction of water with mafic minerals such as olivine and pyroxene common in ophiolites, yields fluids with unusual chemistry (Mg-OH and Ca-OH waters with pH values to ~12), as well as heat and hydrogen gas that can sustain subsurface, chemosynthetic ecosystems. The recent observation of liquid (possibly water?) seeps from pole-facing crater and canyon walls in the higher Martian latitudes supports the hypothesis that even present conditions might allow for a rock-hosted chemosynthetic biosphere in near-surface regions of the Martian crust. The generation of methane within a zone of active serpentinization, through either abiogenic or biogenic processes, could account for the presence of methane detected in the Martian atmosphere. For all of these reasons, studies of terrestrial ophiolite-hosted alkaline springs are particularly timely. Here, we will discuss particular features of ophiolites in general and focus on the Del Puerto Ophiolite in the California Coast Range, where we are studying novel bacteria associated with alkaline springs and streams in which Mg-Ca carbonate cements are precipitating. The carbonates may serve as a biosignature that could be used in the search for evidence of life on Mars.