Earth’s magnetic field sometimes does a flip. The north magnetic pole becomes the south pole, and vice versa. On average, it happens once every few hundred thousand years.

But sometimes, it’s more of a flip flop — the field flips right back over.

One flip-flop took place about 42,000 years ago. Known as the Laschamps Excursion, the flip lasted only a few hundred years. And a recent study said the transition could have been a major problem for Earth’s environment.

The magnetic field protects us from radiation from the Sun and beyond. As the field flips, though, it gets weaker. That allows more radiation to reach the upper atmosphere, where it can zap the ozone layer. In turn, that allows more radiation to reach the surface, where it can cause skin cancers, mutations, and other problems.

During the Laschamps era, the magnetic field dropped to only a few percent of its current strength. Scientists studied the effect of that drop by examining trees buried in New Zealand. The trees’ annual growth rings contained high levels of radioactive carbon — an indication that more radiation was reaching the surface.

The researchers said that the weaker field could have been related to major climate changes, including animal extinctions in Australia.

No other research has reported such dramatic impacts from a flip. So it’s unclear what effect the next flip — or flip-flop — might have on life on our planet.

Script by Damond Benningfield