Containing everything from the ocean basins to continents, the crust is the outermost layer of the Earth. Overall, the crust makes up very little of the Earth's mass, so the other layers, which are the mantle, outer core and inner core, are much thicker.
Metamorphic, igneous and sedimentary rocks appear on the Earth's crust. At most, the crust's thickness is about 45 miles, and beneath that is a section of semi-solid rock, known as the mantle. Beneath the mantle is the Earth's outer core, which is a liquid layer of iron, and the inner core, which is a solid layer of iron and nickel under extreme pressure.