Every few hundred thousand years, Earth’s magnetic poles flip, turning north into south and south into north. These geomagnetic reversals can take thousands of years, but shorter disruptions—called geomagnetic excursions—can occur more frequently and wreak havoc on the planet.

Earth's magnetic field dramatically flipped a little more than 40,000 years ago. We can now experience this epic upheaval, thanks to a clever interpretation of information collected by the European Space Agency's Swarm satellite mission.