When the Earth formed, heavy elements like Iron and Nickel sank to the center, forming a metallic core in a process called "differentiation." This giant metallic and partially-molten ball of metal spins once in 24 hours and has strong convection currents that transport heat upward from deep within our planet. These currents generate the powerful magnetic field that surrounds the Earth. Earth's magnetic field protects us from harmful charged particles from the Sun and helps birds and other creatures navigate. In fact, a spinning liquid metallic core may be a necessary ingredient for the origin of life. For more on the interior of the Earth click here.