Resource Dictionary

Crust

The Earth’s outermost layer—a veneer of solid rock floating atop the partially-molten mantle or inner Earth. The crust is broken into several tectonic plates, which move with respect to each other. Continental crust has a geologic composition similar to granite and averages 40 kilometers in thickness, while crust underlying oceans is mainly composed of basalt and other mafic/ultramafic rocks averaging about 8 kilometers in thickness.