Ocean - Lithospheric Plates And The Origin Of The Seafloor

The oceanic plates beneath the ocean waters and above the earth's mantle are made up of igneous rock, formed from the magma, or molten rock, at mid-oceanic ridges. If you think of the plates as the skin of the earth, then the mid-oceanic ridge system is a 38,000-mile-long (64,000 km) cut in that skin. This cut bleeds lava, and never heals, because as soon as a "scab" of solidified lava develops over it, the two sides are pulled apart—allowing more molten rock to ooze forth into the ocean water. In this way, plates of oceanic crust are formed; one long thin section at a time bonds to the most recently made edges.