Density plays an important role in the study of Earth. It affects Earth's climate, plate tectonics, and subduction.
Subduction occurs at the convergent plate boundaries. Density plays a major role for subduction to take place. Subduction is driven by the excess density of the lithosphere compared to the underlying asthenosphere.
Oceanic plates are denser and colder than continental plates, because the ocean cools them. Subduction can occur between an oceanic plate and a continental plate, or two oceanic plate or two continenetal plates.
During subduction between oceanic and continental plates, mantle convection drags the denser oceanic plate downwards and forces it down into the asthenosphere.
During subduction between two oceanic plates, mantle convection drags the older, denser oceanic plate downwards and forces it into the asthenosphere.
During subduction between two continental plates, there is no mantle convection, because the two plates are of similar densities.
