In the Depths of the Ocean

From National Geographic:

In general, oceanic hydrothermal vents arise when seawater seeps through cracks in Earth’s crust and mingles with hot rocks beneath the surface; those buried molten rocks heat the saltwater and fuel chemical reactions that erupt in a roiling mass through vents in Earth’s crust. The continual extrusion of mineral-rich, superheated seawater provides the heat and energy needed for some organisms to thrive in these cold, dark depths, including a menagerie of vent-specific gigantic tube worms, foot-long clams, blind shrimp, and extreme microbes. 

For a long time, canonical wisdom had suggested that hydrothermal vent activity could only exist at the fastest spreading mid-ocean ridges—places like the East Pacific Rise, where Earth’s tectonic plates are hustling away from one another at speeds of around seven inches a year. At these bursting planetary seams, the brisk spreading of Earth’s crust means that fresh magma is always available to fuel the vents. (Read more.)