Deep-sea hydrothermal vents may produce chimneylike structures made up of sulfides. Known as black smokers, such structures are common on mid-ocean ridges where volcanic activity heats the crust and causes water to circulate through the hot rocks, which leach sulfur and metals that are discharged into the ocean.

Too deep for sunlight, black smokers support ocean ecosystems that derive energy from chemicals in the hot waters rather than the Sun. Life on Earth may have begun under similar conditions.