" This second type of vent is not volcanic, and there’s no magma involved. Instead, it depends on the reaction of these freshly exposed rocks with seawater. Water doesn’t just percolate into such rocks: it physically reacts with them; it is incorporated into them, altering their structure to form hydroxide minerals like serpentine (named after its resemblance to the mottled green scales of a serpent). The reaction with seawater expands the rock, causing it to crack and fracture, which in turn permits further seawater to penetrate, perpetuating the process. The scale of such reactions is astonishing. The volume of water bound into rock in this way is believed to equal the volume of the oceans themselves. As "

― Nick Lane , Life Ascending: The Ten Great Inventions of Evolution