Oceanic crust is denser than continental crust due to differences in their composition and temperature. Oceanic crust is primarily composed of denser mafic rocks such as basalt, formed at higher temperatures near mid-ocean ridges. In contrast, continental crust consists of less dense felsic rocks such as granite and is generally thicker and older.

During plate tectonics processes, when an oceanic plate and a continental plate converge at a convergent plate boundary, the denser oceanic crust is forced to descend below the less dense continental crust through a process called subduction. This process occurs because of the downgoing force of the denser oceanic plate and the resistance of the continental plate to being overridden.

The subduction of oceanic crust plays a crucial role in shaping the Earth's surface features, driving geological processes such as mountain building, volcanic activity, and the formation of arc-trench systems. It also facilitates the recycling of oceanic crust back into the Earth's mantle, contributing to the continuous renewal of the Earth's crustal material.