Earth’s Outer Crust
Rocks and minerals make up most of the outer layer or crust of our earth—the actual ground beneath our feet. The crust is approximately 18 to 30 miles thick beneath the continents. In general, the outermost part consists of many layers of stratified rocks, one above another. The older rocks normally make up the bottom or the deeper layers, and the younger rocks form the upper layers. Not all the layers are perfectly flat and parallel—some are lenticular (lens-shaped), some are tilted, some are partly eroded away, and some are present in one place and absent in another. Beneath the continents, the layers of rock rest on ancient [metamorphic rocks] and on great masses of [igneous] rock such as [granite]. These lower rocks are known as the basement.
Earth’s outer crust (thickness not drawn to scale).
Over much of the land surface of the earth, the outermost layer is made up of layers of rock
On the continents, the layers of rock rest on [metamorphic rocks] and on [igneous] rocks such as [granite]