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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.
This entry comes from Encyclopædia Britannica Concise. For the full entry on seafloor spreading, visit Britannica.com.