<P> One of the most significant correlations discovered to date is that lithospheric plates attached to downgoing (subducting) plates move much faster than plates not attached to subducting plates . The Pacific plate, for instance, is essentially surrounded by zones of subduction (the so - called Ring of Fire) and moves much faster than the plates of the Atlantic basin, which are attached (perhaps one could say' welded') to adjacent continents instead of subducting plates . It is thus thought that forces associated with the downgoing plate (slab pull and slab suction) are the driving forces which determine the motion of plates, except for those plates which are not being subducted . This view however has been contradicted by a recent study which found that the actual motions of the Pacific Plate and other plates associated with the East Pacific Rise do not correlate mainly with either slab pull or slab push, but rather with a mantle convection upwelling whose horizontal spreading along the bases of the various plates drives them along via viscosity - related traction forces . The driving forces of plate motion continue to be active subjects of on - going research within geophysics and tectonophysics . </P> <P> In line with other previous and contemporaneous proposals, in 1912 the meteorologist Alfred Wegener amply described what he called continental drift, expanded in his 1915 book The Origin of Continents and Oceans and the scientific debate started that would end up fifty years later in the theory of plate tectonics . Starting from the idea (also expressed by his forerunners) that the present continents once formed a single land mass (which was called Pangea later on) that drifted apart, thus releasing the continents from the Earth's mantle and likening them to "icebergs" of low density granite floating on a sea of denser basalt . Supporting evidence for the idea came from the dove - tailing outlines of South America's east coast and Africa's west coast, and from the matching of the rock formations along these edges . Confirmation of their previous contiguous nature also came from the fossil plants Glossopteris and Gangamopteris, and the therapsid or mammal - like reptile Lystrosaurus, all widely distributed over South America, Africa, Antarctica, India, and Australia . The evidence for such an erstwhile joining of these continents was patent to field geologists working in the southern hemisphere . The South African Alex du Toit put together a mass of such information in his 1937 publication Our Wandering Continents, and went further than Wegener in recognising the strong links between the Gondwana fragments . </P> <P> But without detailed evidence and a force sufficient to drive the movement, the theory was not generally accepted: the Earth might have a solid crust and mantle and a liquid core, but there seemed to be no way that portions of the crust could move around . Distinguished scientists, such as Harold Jeffreys and Charles Schuchert, were outspoken critics of continental drift . </P> <P> Despite much opposition, the view of continental drift gained support and a lively debate started between "drifters" or "mobilists" (proponents of the theory) and "fixists" (opponents). During the 1920s, 1930s and 1940s, the former reached important milestones proposing that convection currents might have driven the plate movements, and that spreading may have occurred below the sea within the oceanic crust . Concepts close to the elements now incorporated in plate tectonics were proposed by geophysicists and geologists (both fixists and mobilists) like Vening - Meinesz, Holmes, and Umbgrove . </P>

What is the mechanism behind the movement of earth's tectonic plates