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A shipboard microbiology laboratory to investigate the extent and diversity of the subsurface biosphere in the ocean basins is being developed by the Ocean Drilling Program (ODP) and may soon provide answers to some of the exciting questions about Earth's deep biosphere. The answers may also be relevant to explorations for extraterrestrial life.

The oceanic subsurface biosphere may contain half of Earth's biomass [Whitman et al., 1998]. Each liter of deep sea sediment, even at depths of a kilometer below the seafloor, typically contains more than 1 billion microbes. Volcanic rocks below the sediment also appear to contain microbes at all depths investigated so far, except where the temperature exceeds 100°C. Although microbes probably contribute less than a gram of biomass per cubic meter of oceanic crust, the vast amount of oceanic sediment and rock makes the total microbial biomass globally significant.