Why do the North and South Poles swap their magnetic polarity?
The Earth has two magnetic poles, the North and South Poles, where the magnetic fields generated from the spinning molten core come to their "North-South" orientation. This is true North-South as accepted by compass readings, not the geographic North and South Poles. It is believed because of historical and other data that due to the nature of planetary rotation, the two Magnetic Poles have "wandered" in the past to orient themselves around the greatest spinning mass, and even have swapped entirely. This sort of movement, during which the entire crust and mantle of the planet shifts around the magnetic axis (along which the planet rotates) is believed to be responsible for some extinction events. While the science is evidence-based, pole shifts and True Polar Wander events take thousands of years to complete, meaning that the Earth may have time to adjust to a new polar orientation if such a thing occurs, though shifts may have been responsible for some extinction events. A fast and destructive polar reversal, such as depicted in doomsday scenarios and films, is impossible.