The CORE is the central part of the Earth. It is made up of two distinct parts, the inner CORE and the outer CORE. The inner CORE is a solid ball of iron and nickel that is about 1, 500 miles in diameter. The outer CORE is a liquid layer of iron and nickel that surrounds the inner CORE and is about 1, 400 miles thick. The CORE is the hottest part of the Earth, with temperatures reaching up to 9, 000 degrees Fahrenheit. It is also the densest part of the Earth, with a density of 13.1 grams per cubic centimeter.