What is the earths crust purpose?

The earth's crust protects the flora and fauna that inhabit the surface from the molten interior.

Earth's crust. The crust of the Earth is composed of a great variety of igneous, metamorphic, and sedimentary rocks. The crust is underlain by the mantle. The upper part of the mantle is composed mostly of peridotite, a rock denser than rocks common in the overlying crust.