Inner core
The inner core is the deepest of the layers, the center of the Earth. It's only about 1,500 km thick. It's made out of solid and heavy materials such as iron. It is possible, scientists believe, that the inner core could have a temperature similar to the Sun's surface (9806 F˚). The existence of a solid inner core apart from the distinct outer core was realized in 1936 by a seismologist. He used observations of earthquake-generated seismic waves that partly reflect from its boundary and can be detected by sensitive seismographs on Earth's surface.