<P> Earlier theories ( e.g. by Alfred Wegener and Alexander du Toit ) of continental drift postulated that continents `` ploughed '' through the sea . The idea that the seafloor itself moves ( and also carries the continents with it ) as it expands from a central axis was proposed by Harry Hess from Princeton University in the 1960s . The theory is well accepted now , and the phenomenon is known to be caused by convection currents in the asthenosphere , which is ductile , or plastic , and the brittle lithosphere ( crust and upper mantle ) . </P>
what observation led to the theory of seafloor spreading
that continents `` ploughed '' through the sea .