Microbes are the major mediators of biogeochemical cycles on earth. Initial work indicates that a potentially high biomass and active microbial biosphere exists in the subseafloor ocean crust that lies below seafloor sediments, but data is currently limited to a few sites and studies. Likewise, seafloor exposed ocean crust at mid-ocean ridges, inactive hydrothermal sulfides and hydrothermal plumes are also globally distributed microbial substrates that host a potentially large biomass. For all these habitats, the magnitude and diversity of the microbial community and rates of biogeochemical transformations are currently unconstrained. I utilize biogeochemical analyses, traditional microbiological techniques, mineralogy, geochemistry and and molecular biology to better understand
