The Earth has two solid parts: the outer crust that covers the surface, and the inner core, which is primarily made of iron. Earth has three layers that make up nearly 4,000 miles of rock, solid metals and liquid metals.
The crust is the part of the Earth that includes volcanoes and tectonic plates. It is situated above the viscous mantle. The Earth has a two-part core, with a liquid outer layer and a solid inner layer. The outer core is made of iron and nickel. The inner core is made mostly of iron because the metal is heavier than the other materials that make up the other layers. The pressure from the layers above the inner core prevent the iron from melting.