* Density: Continental crust is less dense than oceanic crust. This is due to the presence of more silica and aluminum, making it more "granitic" in composition. Oceanic crust is denser because it's more "basaltic," with more magnesium and iron.
* Buoyancy: The difference in density plays a key role in buoyancy. Less dense materials float higher, much like a piece of wood floats higher in water than a piece of metal.
* Isostasy: The concept of isostasy describes the balance between the weight of the Earth's crust and the upward buoyant force of the mantle. Continental crust, being less dense, will displace a greater volume of the denser mantle to achieve this balance.
Therefore, a certain thickness of continental crust will actually displace *more* of the mantle than the same thickness of oceanic crust.
Think of it this way: Imagine a block of wood and a block of metal, both the same size. You place them in a pool of water. The wood block will float higher, displacing more water than the metal block, even though they are the same size. The same principle applies to the Earth's crust.
Important Note: While continental crust displaces more mantle overall due to its lower density, the *depth* of the roots of mountains in the mantle is less than the depth of oceanic crustal plates. This is because the thickest continental crust forms mountain ranges, which are compensated by deeper roots.
