How did harry hess's hypothsis explain seafloor movement?

It explained seafloor movement because he researched that hot/less dense material rises to Earths crust, at the Mid-Atlantic Ridge. At the hole the magma cools making new seafloor. He also found out that there were new rocks near the Mid-Atlantic Ridge and old ones farther away. Hess also theorized that this seafloor has to filter somewhere- this somewhere is called the subduction zone. The subduction zone is an area where old seafloor sinks and the plates melt it forms into magma, building pressure within the Earth. When there is too much pressure the Earth lets out this energy in Arcs, Volcanic islands, etc.