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Definition of SEAFLOOR SPREADING
: the divergence at mid-ocean ridges of the tectonic plates underlying the oceans that is due to upwelling from the earth's interior of magma which solidifies and adds to the spreading plates
First Known Use of SEAFLOOR SPREADING
Theory that oceanic crust forms along submarine mountain zones, known collectively as the oceanic ridge system, and spreads out laterally away from them. This idea, proposed by U.S. geophysicist Harry H. Hess (1906–1969) in 1960, was pivotal in the development of the theory of plate tectonics.