Definition (Encyclopedia of Global Resources)
Seafloor spreading is the process by which the seafloor splits and new oceanic crust is created. The ocean basins are enlarged by the movement of molten basalt (magma) through cracks in a centralized oceanic ridge system, such as the Mid-Atlantic Ridge.
(The entire section is 41 words.)
Overview (Encyclopedia of Global Resources)
During the 1950’s and 1960’s, oceanographic studies revealed that the seafloors of the Earth were marked by a nearly continuous system of submarine ridges, more than 40,000 kilometers in total length. Detailed investigation revealed that this mid-oceanic ridge system has a central rift valley that runs along its length and that the ridge system is associated with volcanic and earthquake activity. Magnetic studies of the seafloor indicated that the oceanic lithosphere (Earth’s oceanic crust and part of the upper mantle) was segmented into long, magnetic strips parallel to the axis of the mid-oceanic ridges. Furthermore, on either side of the ridge, the floor of the ocean was found to consist of alternating bands of rock: Rocks that are magnetized parallel to the present-day direction of Earth’s magnetic field alternate with rocks magnetized exactly opposite to Earth’s present-day field direction.
Integrating these data, Henry Hess postulated in 1960 that the mid-oceanic ridges are tensional features representing zones of weakness within the Earth’s crust and that new seafloor is created by the welling up of mantle material into cracks along the ridges, followed by lateral spreading. Hess hypothesized that the mantle is capable of plastic flow and that the ridges represent the meeting place of two rising convection currents of molten rock material from within the mantle. As rifting proceeds, magma ascends to fill in the...
(The entire section is 463 words.)