Continental and oceanic crust are both destroyed in subduction zones and lie atop Earth's mantle, though they differ in thickness, density, age and chemical composition. A subduction zone is an area of Earth's crust where tectonic plates meet.
The oceanic crust is thinner, denser and younger than the continental crust. It is the outermost layer of Earth's lithosphere and is found under oceans. It is formed at divergent plate boundaries on oceanic ridges. The oceanic crust is about 4 miles thick and is composed of several layers of lavas made of basalt, diabese and gabbro. Oceanic crust can be aged up to 200 million years. Because oceanic plates are denser than the buoyant continental plates, they are the ones that sink, or subduct, when the two plates converge, according to the National Park Service.
Continental crust is about 22 miles thick and has a surface elevation of 3 miles above the ocean floor. The structure and origin of continental crust is more complex than that of oceanic crust. As oceanic plates subduct beneath continental plates, rock is scraped off the top of oceanic plates and built up, causing lateral growth of the continental crust. These subduction zones are often marked by volcanoes. The age of the continental crust is almost two billion years. The continental crust is composed of slightly less dense rock, such as granite.