A mid-ocean ridge is an extensive underwater mountain range that marks a divergent plate boundary where tectonic plates are pulling apart. These immense geological features are sites of active seafloor spreading, driven by magma rising from the Earth's mantle to fill the widening gap between the plates. The upwelling magma cools and solidifies, creating new oceanic crust and resulting in highly active volcanism and frequent seismic activity. The sheer scale of these ridges influences ocean currents and global plate movement, providing essential evidence of plate tectonics theory.