There are 4 main layers of the earth. The crust, the mantle, the outer core and the inner core.  The crust is the thinest layer in the earth. It is made of thick rock and is 4-7 miles. The mantle is thickest layer. It is 1,800 miles deep. It is made of soft molten rock and lava. The outer core is 1,370 miles. It is made of liquid iron. The inner core is the size of mars. It is 780 miles deep. It is made of mostly iron.