There are few things as reliable in life as north and south, right? Wrong, say UC Berkeley researchers – magnetically speaking, that is. Though scientists have known that Earth’s polarity has the potential to change over time, a new study suggests that at least once in Earth’s history, it changed in less than 100 years.

“It’s amazing how rapidly we see that reversal,” said UC Berkeley graduate student Courtney Sprain. “The paleomagnetic data are very well done. This is one of the best records we have so far of what happens during a reversal and how quickly these reversals can happen.”

The rapid flip happened about 786,000 years ago, they say. Now, new data suggest shows that the strength of Earth’s magnetic field is decreasing 10 times faster than normal, leading some scientists to believe that we could experience yet another polarity change in the next few thousand years. The evidence comes from Italy, where researchers measured the magnetic field directions frozen into the sediments as they accumulated at the bottom of the ancient lake.

Though there are no known instances of changes in the magnetic field causing disaster, modern times are different. Currents created during the switch could bring down the power grid, while the weakened magnetic field could expose Earth to cosmic rays and solar energy particles.

Though a rapid reversal without warning is possible, it’s unlikely – evidence shows that the previous flip was preceded by a period of magnetic instability that spanned 6,000 years.