It's divided into two parts:

* Inner core: A solid ball of mostly iron and nickel, about 1,220 kilometers (758 miles) in radius. The immense pressure at the center of the Earth keeps it solid despite the incredibly high temperatures (around 5,200° Celsius or 9,392° Fahrenheit).

* Outer core: A liquid layer of iron and nickel, about 2,200 kilometers (1,367 miles) thick. The liquid outer core is responsible for generating Earth's magnetic field.

While we can't directly observe the Earth's core, scientists have learned about it through studying seismic waves from earthquakes and by analyzing the composition of meteorites.