Hydrothermal vents form where tectonic plates pull apart at mid ocean ridges. Seawater seeps into the crust, is superheated by magma to as much as 464 degrees Celsius, and is kept from boiling by the weight of the ocean above, becoming a supercritical fluid that strips sulfur, iron, copper, and zinc from the rock. When it hits water near two degrees Celsius, the metals precipitate instantly. Black smokers build sulfide chimneys up to 60 meters tall at up to 30 centimeters a day, while cooler white smokers release barium, calcium, and silicon. Their plumes spread for thousands of kilometers, carrying iron and manganese through the ocean, and researchers find vents by sniffing for helium-3 and radon-222. Since the first vents were found in 1977, biologists have mapped food webs built on chemosynthesis, in which bacteria draw energy from toxic hydrogen sulfide.

Alkaline vents are a leading candidate for where life began. Pockets of supercritical carbon dioxide could shelter early molecules from water that breaks them apart, and the proton gradient between alkaline vent fluid and the acidic ancient ocean works like a battery across porous iron sulfur rock. Tube like microfossils from the Nuvvuagittuq Belt in Quebec may date to 4.28 billion years ago, and vent plumes have been detected on Europa and Enceladus. The same chimneys hold seafloor massive sulfide deposits rich in copper, gold, zinc, and rare earth metals, and Japan completed the first large scale mining test on one in 2017.

• Giant tube worms, Riftia pachyptila, grow over six feet tall with no mouth or gut, farming bacteria in an organ called the trophosome.
• Zinc in the worms’ blood binds sulfide so it cannot poison the hemoglobin carrying oxygen.
• The scaly foot snail builds armor from iron sulfide to fend off venomous cone snails.
• A chimney nicknamed Godzilla off Oregon reached the height of a 15 story building before collapsing in 1996.
• Vent animals still depend on oxygen made by surface photosynthesis, so they are not fully independent of the sun.