Which force is responsible for seafloor spreading? A. gravity in the mantle B. convection in the mantle C. the effect of tides D. convection in the crust

Earlier theories (e. g. by Alfred Wegener and Alexander du Toit) of continental drift were that continents ploughed through the sea. The idea that the seafloor itself moves (and 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 plastic, very weak upper mantle, or asthenosphere.