Final answer:
The true statement is that oceanic crust is denser than the continental crust due to its composition, primarily of basalt, compared to the continental crust's composition, predominantly of granite, which is less dense.
Step-by-step explanation:
The statement that oceanic crust is denser than continental crust is true. Oceanic crust is composed mainly of basalt, which is a volcanic rock with a high content of silicon, oxygen, iron, aluminum, and magnesium, resulting in a higher density. In contrast, continental crust is generally comprised of granite, a volcanic rock with a high silicon and oxygen content, but less dense than basalt. The thickness of continental crust varies significantly and can be much thicker than oceanic crust, but it is still less dense overall. The dense oceanic crust can subduct beneath the lighter continental crust at subduction zones, a process that helps to balance the creation and destruction of crustal material along earth's rift zones and ocean trenches.