Mid-ocean ridge
A continuous underwater mountain chain, about 65,000 km long, marking divergent plate boundaries where new oceanic crust is created.
Magma chamber: A reservoir of molten rock beneath a volcano or rift, feeding eruptions and intrusions. Melt rising beneath the ridge axis crystallizes to form the lower crust and gabbro layer.
Mid-Atlantic Ridge: A slow-spreading ridge bisecting the Atlantic Ocean, running from the Arctic to the Southern Ocean. The ridge mapped by the Heezen–Tharp physiographic diagrams that made seafloor spreading plausible.
Marie Tharp: Oceanographic cartographer who, with Bruce Heezen, drafted the first full physiographic map of the ocean floor. Her 1950s profiling of Atlantic echo soundings revealed the ridge's continuous rifted crest.
Subduction zone: A convergent boundary where oceanic lithosphere bends and descends into the mantle beneath another plate. The ridge creates oceanic lithosphere; subduction zones are where that lithosphere is consumed.
Vine–Matthews–Morley hypothesis: The 1963 proposal that symmetric magnetic stripes on the seafloor record reversals recorded during spreading. The stripes flank the ridge axis symmetrically, which converted spreading from hypothesis to fact.
Hydrothermal vent: A seafloor opening that discharges seawater heated by underlying magma, often as chimney structures. Seawater circulates through fresh ridge crust and exits at vents like black smokers.
East Pacific Rise: A fast-spreading ridge in the eastern Pacific, spreading at up to 15 cm per year. Its broad, shallow, valley-free axis showed how spreading speed reshapes ridge topography.
HMS Challenger expedition: The 1872–1876 circumnavigation that performed the first systematic deep-sea sounding and sampling campaign. Its soundings gave the first hint of a raised mid-Atlantic swell before the ridge was recognized.
Continental rift: A zone where a continent is stretched and thinned, often with volcanism, prior to possible ocean formation. Continental rifting is the early stage; a mid-ocean ridge is the mature oceanic version.
Deep biosphere: Microbial life living in the pores and fractures of rock beneath the seafloor and ocean crust. Ridge hydrothermal circulation supplies chemical energy that feeds subsurface microbial ecosystems.