Evidence Shows Earth's Magnetic Field Once Flipped Very Quickly 

By Ryan F. Mandelbaum on at

A new study analysing rock formations from 107,000 to 91,000 years ago has revealed something troubling: a strangely quick reversal of the Earth’s magnetic field in fairly recent history.

The team of researchers from China, Taiwan, and Australia analysed a stalagmite, a rock that slowly grows up from the floors of caves, in order to get a better understanding of Earth’s magnetic field. In iron fragments from the rock, they found evidence of a flip that happened in under 200 years. It’s not clear what would happen to humanity if the magnetic field were to reverse again over such a short timescale. The scientists behind the new paper worry it could be bad.

“If such rapid polarity changes occurred in future, they could severely affect satellites and human society,” they wrote in the paper published this week in the Proceedings of the National Academy of Sciences.

If the Earth’s magnetic field confuses you, worry not, because it confuses lots of scientists, too. It seems to have existed for at least 3.45 billion years, and is probably generated through motion in Earth’s outer core. The north and south poles seem to have reversed around 773,000 years ago, and perhaps a dozen excursions, or quick changes to the poles’ angles of orientation, have occurred since then, according to the paper.

Naturally, people worry about the poles shifting because of the magnetic field’s protective effects. It shields us from the solar wind, which might harm both life on the planet and our electronics.

In this most recent study, scientists analysed a stalagmite called SX11, taken from the Sanxing Cave in Guizhou Province, China. It’s 1 metre (3.3 feet) long, 8 centimetres (3 inches) around, and looks like a yellow-and-brown candle. The team cut 194 slices from it, dated the slices, and measured the magnetic field orientation from the leftover fragments of iron captured in the rock.

The team’s analysis revealed evidence of quick magnetic pole changes, including one reversal starting around 98,360 years ago that took only 144 years, give or take 58 years.

“That’s shockingly fast,” Mika McKinnon, a geophysicist (and former Gizmodo writer) who was not involved with the study, told Gizmodo. From a scientific standpoint, she was excited about the results. “Researchers have been using speleothems,” cave deposits like stalagmites, “to reconstruct magnetic field reversals since before I was born, but it’s still a rare technique to encounter and I’m always charmed.”

She pointed out that factors like heat can cause the cores to demagnetise, and researchers have explained away previous evidence for quick pole reversals. “Time will tell if researchers do the same with this data, too.” The authors behind the new paper call for an improvement in studies of previous magnetic field changes in order to better understand the potential for a magnetic field reversal.

Should you be worried? Well, just because the magnetic fields can flip doesn’t mean that they will any time soon, as we’ve written previously.

It’s also not entirely clear what would happen during one of these pole reversals, said McKinnon. “We know the magnetic field weakens as it transitions, dropping to just 5% or less of its usual strength. Some scientists think it collapses entirely.” But perhaps the solar wind itself would regenerate the field. Maybe it will harm our technology, but not us — there isn’t firm evidence linking these field reversals to mass extinctions, for example.

So, it’s probably not worth getting upset about. Said McKinnon: “I’ll stick with the optimistic interpretation that living through a rapid magnetic field reversal would be a period of glorious chaos, but not deadly.” [PNAS]

Feature illustration: NASA (Air Force)