Earth’s Magnetic Poles Can Trade Places

The place your compass points is not fixed. It wanders year by year, and every so often in deep time, the magnetic poles flip.

Earth’s magnetic field comes from molten iron moving in the outer core. That is a turbulent process, so the field shifts. The north magnetic pole, which sat in Canada for most of the time people have tracked it, has moved across the Arctic Ocean toward Siberia. Navigation systems depend on a model of the field that gets updated every five years.

Written in stone

When lava cools, tiny magnetic minerals inside lock in the direction of the field at that moment. Geologists can read these layers like pages. They show that the poles have reversed many times, most recently about 780,000 years ago.

A small physics twist

The north end of a compass needle is attracted to a south magnetic pole. So in strict physics terms, the thing we call the north magnetic pole behaves as a magnetic south pole. The names came from geography first, and nobody has felt like redoing the maps.