A continuous, seismic, median mountain range extending through the North and South Atlantic Oceans, the Indian Ocean, and the South Pacific Ocean. It is a broad, fractured swell with a central rift valley and usually extremely rugged topography; it is 1 to 3 km in elevation, about 1,500 km in width, and over 84,000 km in length. According to the 1985 hypothesis of sea-floor spreading, the mid-ocean ridge is the source of new crustal material.