evidence: Many times over our planet’s history, Earth’s magnetic poles have reversed, meaning that sometimes a compass pointing north will be aimed at Antarctica rather than the Arctic. This might sound strange, but it’s a relatively predictable quirk. Powered by the machinations of the planet’s spinning iron core, this process of geomagnetic reversal has been doing its thing without much fanfare for eons. [...] If geologic history repeats itself, Earth’s magnetic poles should eventually swap places. This much is undeniable. Based on the magnetic fingerprints locked into ancient rocks, we know that over the last 20 million years, magnetic north and south have flipped roughly every 200,000 to 300,000 years (this rate has not been constant over the planet’s lifetime, though). The last of these major reversals occurred about 780,000 years ago, although the Poles do wander around in between these larger flips. (What’s more, climate change seems to be shifting Earth’s geographic poles.) [...] Also unclear. Scientists estimate that past polar flips have been rather sluggish, with north and south migrating to opposite positions over thousands of years. This is both good and bad if you’re concerned about how a geomagnetic reversal will affect life on Earth.