Earth’s core is located below the middle layer called the mantle and the outer layer –or crust. It consists of two main parts–a liquid outer core and a more solid inner core. The outer layer is made of liquid iron-nickel and is responsible for producing Earth’s magnetic field.

Scientists of course cannot cut into Earth and directly observe its insides. Instead, their knowledge is inferred from the vibrations generated by earthquakes that pass through the planet. The speed and the direction of the seismic vibrations change depending on the density and the elasticity of the rocks.

At the center of our planet is a very hot rotating ball of mostly iron and nickel (sorry Journey to the Center of the Earth fans). Scientists infer features of this innermost geographic layer—like the fact that it’s divided into a liquid outer core and a solid inner core—by analyzing how it distorts seismic waves caused by earthquakes.