Inner Core
The inner core is known as the innermost hottest part of the earth. It is a solid ball which is about 1,200 km in radius . It contains iron and nickel and can have the temperature similar to the sun's surface which is about 5,505 Celsius.
http://en.wikipedia.org/wiki/Inner_core
http://en.wikipedia.org/wiki/Inner_core
http://www.kidsgeo.com/images/earths-inner-core.jpg