In October 2010, an international team of scientists set sail on the scientific drilling vessel JOIDES Resolution for an eight- week expedition to the South Pacific. There, we penetrated a total of 630 m at seven different drill sites to define the physical and chemical limits of subseafloor microbial life in tectonic and oceanographic settings not yet explored!

We (1) documented habitats, activities, composition, and biomass of microbial communities in subseafloor sediment with very low total activity and very low biomass, (2) determined oceanographic controls on sedimentary habitats, activities, and communities from gyre center to margin, (3) constrained the extent that the subseafloor communities are nourished by hydrogen produced in situ by water radiolysis, and (4) determined how basement habitats, potential activities, and communities vary with crustal age and hydrologic regime and evolve over 100 million years in a region of fast seafloor spreading and very low sedimentation rate.