Question: where do seafloors with older ages tend to be found

title: Seafloor spreading
text: In the general case , sea floor spreading starts as a rift in a continental land mass , similar to the Red Sea - East Africa Rift System today . The process starts by heating at the base of the continental crust which causes it to become more plastic and less dense . Because less dense objects rise in relation to denser objects , the area being heated becomes a broad dome ( see isostasy ) . As the crust bows upward , fractures occur that gradually grow into rifts . The typical rift system consists of three rift arms at approximately 120 degree angles . These areas are named triple junctions and can be found in several places across the world today . The separated margins of the continents evolve to form passive margins . Hess ' theory was that new seafloor is formed when magma is forced upward toward the surface at a mid-ocean ridge .