A mid-ocean ridge (MOR) is a submarine mountain range with a valley (rift) at its center. A MOR corresponds to the divergent margin of two tectonic plates (divergent plate boundary). Here the Earth’s crust is spreading, forming new ocean floor that gradually moves away from the ridge at a speed between 2 and 10 cm per year. Beneath a MOR, mantle material partially melts as it rises in response to reduced pressure. Produced magma is collected in a magmatic chamber a few kilometers below the seafloor. Much of the magma eventually freezes in place forming the bulk of the new oceanic crust (basalts and gabbros). Seawater circulates actively, reacting with the volcanic rock, dissolving out metals, and depositing them around seafloor hot springs. Fractures filled with heated water act as incubators for microbes that live in some of the harshest conditions ever discovered to support life. Conditions typical at MOR have been often depicted as one of the possible...