We all know that North is, well, north—somewhere above Alaska—and south is down near the middle of Antarctica. That will always be true for the planet’s geographic poles, but it’s only intermittently true for the planet’s magnetic poles. Over the past 20 million years, the magnetic poles have flip-flopped every several hundred thousand years or so, which means that if you had a compass in hand about 800,000 years ago, it would tell you that north was in Antarctica.
Though scientists are pretty sure Earth’s churning, molten iron core powers these polar acrobatics, it’s not entirely clear what triggers the actual reversals. The process is gradual and occurs over millennia. For now, Earth’s north magnetic pole is creeping northward by about 40 miles a year. And given that the last major pole reversal happened 780,000 years ago, we are overdue for a flip.