Earth's magnetic poles flipped some 41,000 years ago; here's how

Earth's magnetic field serves as a protective barrier against cosmic radiation from space. But this shield isn't always as stable as it appears.

There are some short-lived episodes when the magnetic north wanders, occasionally switching with the south pole. This natural process, known as magnetic field excursions, reduces the strength of the magnetic field. 

One well-known example of a magnetic field excursion is the Laschamps event, which happened around 41,000 years ago. Along with the upside-down compass, this occurrence dramatically weakened the strength of Earth's magnetic field.