The metal returns up the outer cylinder, and electric currents create a magnetic field.

BBC: Planet Earth

The inner core, made of very pure, solid iron, rotates along with the outer core, dragging the Earth's magnetic field with them.

BBC: Earth's wobbles reveal deep secrets

The research could help test simulations of how the outer, fluid core generates the Earth's magnetic field, which shields our planet and the teeming life on it from harmful cosmic rays.

BBC: NEWS | Science/Nature | Earth's core runs ahead of crust