The deep ocean floor, once assumed to be a featureless desert, is now recognized as one of Earth's most ecologically complex environments. Hydrothermal vents — fissures in the seafloor through which geothermally heated water erupts — support thriving ecosystems entirely independent of solar energy. At these vents, discovered near the Galapagos Rift in 1977, communities of tube worms, clams, shrimp, and microbial mats flourish in water temperatures that can exceed 400 degrees Celsius at the vent opening, though organisms typically inhabit cooler peripheral zones.

The energy source sustaining these communities is chemosynthesis, carried out primarily by bacteria and archaea. Unlike photosynthesis, which converts light energy into chemical energy, chemosynthesis harnesses the energy released by oxidizing inorganic compounds — principally hydrogen sulfide — to fix carbon dioxide into organic matter. These microbes form the base of the food web, either living freely in the water column or colonizing the tissues of larger invertebrates in mutualistic symbiosis. Giant tube worms, for instance, lack digestive systems entirely; they harbor chemoautotrophic bacteria in a specialized organ called the trophosome and absorb nutrients produced by their microbial partners.

The discovery of hydrothermal vent ecosystems profoundly altered scientific thinking in two respects. First, it demonstrated that life does not require sunlight, expanding the definition of the biosphere and fueling speculation about life in subsurface oceans on icy moons such as Europa and Enceladus. Second, extremophile microbes found at vents — surviving high temperatures, pressures, and toxic chemical concentrations — have challenged the assumption that complex biochemistry requires mild conditions. Enzymes isolated from vent organisms have found industrial applications in DNA amplification and other biotechnological processes, because of their ability to function at temperatures lethal to most life.