human
I've heard that the Earth has a natural magnetic field. What is this?
assistant
The Earth's magnetic field is a natural phenomenon caused by the rotation of the Earth on its axis. It is generated by the movement of molten iron in the outer core of the planet. The magnetic field is strongest at the poles, where it can be as strong as 20,000 to 30,000 nanoteslas (nT). At the equator, the magnetic field strength is about 1/10th as strong.