Evolution of the ocean bottom according to the expanding earth hypothesis is represented by these diagrams. Top layer of material is sedimentary rock of continents. Below it is the type of material that makes up the crust of the oceans. Bottom layer (vertical hatching) is the earth's mantle. In top diagram, continents are close together; rift between is just opening up. Next, material from mantle comes through rift, creating mid-ocean ridge seen in third diagram. Bottom diagram represents Atlantic ocean bottom as it is today, with ridge and rift in center and continents at far right and left. Heezen, 1960.