The discovery of high-temperature (“black smoker”) hydrothermal vents at sea-floor spreading centers in the late 1970s was a revelation. Fluids at temperatures of 300–400°C (572–752°F) exit these vents and mix with the overlying ocean, creating spectacular mineral deposits and allowing development of unusual ecosystems. Hydrothermal vents have since been found along many sections of the global mid-ocean ridge (MOR) system, a 60,000-km (37,280-mi) chain of undersea volcanoes that circles the Earth like the seams on a baseball. MORs are places where new tectonic plates are created, so there is plenty of magma and heat available in these locations to drive hot, reactive fluids through the crust.