The Earth's core is made up primarily of the metals nickel and iron. The inner core is mostly iron, while the outer core is composed of both nickel and iron.
The inner core is very hot at 9,000 to 13,000 degrees Fahrenheit, however, the iron is not liquid because of the pressure of the Earth pressing in on it. It is this solid center that creates the Earth's magnetic field, which is also responsible for the magnetism of the North and South Poles. The outer core is also hot, but not quite as hot as the inner core, at 7,200 to 9,000 degrees Fahrenheit.