A hydrothermal environment is a setting dominated by the circulation of hot, mainly aqueous fluids. In a mid-ocean ridge setting, seawater penetrates the crust, becomes heated, interacts with the crust so that its composition changes, then exits the crust at a hydrothermal vent on the ocean floor. The environment surrounding the vent sustains rich, anoxic chemotrophic ecology. This environment is a possible setting for the emergence of life on Earth.

The simple definition of a hydrothermal fluid is a hot water-rich fluid in the Earth’s crust. The origin of the fluid is diverse, ranging from seawater that penetrates down into the oceanic crust or fills pore space in sedimentary basins to magmatic fluid released from crystallizing igneous intrusions. These fluids are heated as they descend into the crust or come into contact with magmas. Hot fluids are capable of transporting large volumes of material derived from the parent magma or leached from surrounding rocks,...