ENERGY, ENVIRONMENTS, AND DIVERSTIY AT DEEP-SEA HYDROTHERMAL VENTS

Since their discovery in the late 1970's, a growing understanding of energy sources and environments in deep-sea hydrothermal systems has led to an appreciation of the chemical and thermal extremes at which life can exist. While black smokers are the de facto totems of hydrothermal systems, the range of environmental regimes that support primary production in the deep sea is noteworthy, and includes off-axis low-temperature systems, flange pools, subsurface habitats, plumes, sediment-hosted systems - all of which may occur across large gradients of depth and include diverse chemistries. The catalog of potential and known metabolic types at hydrothermal systems captures the profound notion that where water and a disequilibrial redox condition exists, so too will life, at least to the bounds of temperature where biochemical constituents no longer retain their structural and functional integrity. Genomic libraries of hydrothermal microorganisms deeply rooted in the tree of life may provide insight into the biogeochemical evolution of life on Earth, especially when placed within the context of a nearly 4-billion-year geochemical history recorded in hydrothermally altered rock. From our knowledge of hydrothermal systems on Earth, we expect that extremophiles, even those anaerobic ones that eke out a living on energy-poor substrates, can occur in sufficient abundance to leave their imprint in biochemical and mineral fossils.