Seafloor spreading is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge. Seafloor spreading helps explain continental drift in the theory of plate tectonics.
Denser materials sank to the earths center and less dense materials were forced to the outer layers, forming a thin crust. Atmosphere: Less dense molecules rose to the surface. Oceans: As earth cooled, water vapor condensed to form rain which lead to the formation of oceans.
