* Outer core: This is a liquid layer about 2,200 kilometers (1,367 miles) thick. It is mostly made up of iron and nickel, with small amounts of sulfur, silicon, and oxygen. The extreme heat and pressure in the outer core cause these elements to melt.

* Inner core: This is a solid sphere with a radius of about 1,220 kilometers (758 miles). It is also mostly iron and nickel, but the intense pressure at the center of the Earth is so great that it keeps the metals from melting, even though the temperature is higher than the surface of the sun.

So, the Earth's core is a combination of liquid (outer core) and solid (inner core).