Hydrothermal Vent

A hydrothermal vent is an opening in the seafloor, usually near a mid-ocean ridge, from which water heated by magma flows out. Vents support dense communities of animals that live without sunlight, using chemical energy instead.

Cold seawater seeps through cracks in the crust near a spreading center, where plate tectonics opens the seafloor. It is heated by hot rock, picks up dissolved metals and sulfur, and rises again. Where the hot fluid meets cold water, minerals precipitate to form chimneys. "Black smokers" release fluid at up to about 400 °C, which stays liquid because of the pressure of the deep ocean.

Vents were first seen in 1977, when the submersible Alvin visited the Galápagos Rift. The base of the food web is made of bacteria and archaea that gain energy from chemicals such as hydrogen sulfide, a process called chemosynthesis. Animals such as the giant tube worm host these microbes inside their bodies, while the Pompeii worm and the yeti crab live around the chimneys. Many of the microbes are extremophiles.

Vents are a leading candidate for the setting where life began. Alkaline vents, such as the Lost City field found in 2000, produce natural proton gradients across thin mineral walls, similar to those used in chemiosmosis, and the reactions of methanogenesis may have been an early energy source. These ideas are discussed under abiogenesis.

• Giant Tube Worm — an animal of the vents
• Abiogenesis — the origin-of-life hypotheses involving vents
• Extremophile — organisms that live in such conditions