Geological studies have shown that the geomagnetic field has reversed 10 times in the last 2.6 million years alone. The last time was about 780,000 years ago — an event known as the Brunhes-Matuyama reversal.
But although the process is linked to movements in the molten core, it isn’t well understood — and scientists aren’t sure when the next reversal will occur.
“The Earth’s magnetic field reverses on average every 300 to 400 thousand years,” explained Adrian Muxworthy, a professor of Earth and planetary magnetism at Imperial College London who wasn’t involved in the study. “But it’s chaotic. It isn’t regular. There have been periods where it hasn’t reversed for up to 30 million years, but we’re kind of due one.”
The geological records of previous reversals show it can take 500 to 2,000 years for the Earth’s magnetic field to completely reverse by growing gradually weaker in the prevailing direction and gradually stronger in the opposite direction, he said.