The Earth's magnetic poles are not fixed over geological time. As the Earth spins on its axis its molten iron core naturally produces an electrical and magnetic field which gives the planet its magnetic north and south poles. The earth's magnetic field continuously and irregularly varies, and from time to time it flips completely, causing the magnetic north and south poles to trade places, a phenomenon known as palaeomagnetic reversal. Palaeomagnetic reversals have occurred many times over the Earth's history, the last one occurring about 780,000 years ago.
