We owe our existence to the Earth's magnetic field, the invisible barrier that protects the planet from the harsh radiation of space. But this shield is far from static, and tends to wane and even reverse at semi-regular intervals. With the magnetic field currently weakening, there's been a lot of talk in recent years that another flip might be imminent, but a new study has looked at the history of these events and found that a reversal probably isn't about to happen.
The cause for concern starts with what's known as the South Atlantic Anomaly (SAA). In this area, stretching across the Atlantic Ocean from Chile to Zimbabwe, the magnetic field is substantially weaker than elsewhere in the world. Ever since this region was discovered in 1958, it's been growing, as part of an overall weakening of the entire magnetic field over the last few centuries.
The end result of that trend appears to be the reversal of the poles. Historically, magnetic north and south switch places every 200,000 to 300,000 years, and we're actually well overdue for such an event – it's been about 780,000 years since the last one. Although doomsayers love to shout about how a pole reversal would rain down hellish amounts of radiation onto Earth, NASA says that our biggest concern would just be buying new compasses.
But how likely is that scenario, anyway? To find out, researchers from the University of Liverpool, GFZ German Research Center for Geosciences and the University of Iceland looked to past fluctuations in the field. A weakening magnetic field doesn't always mean the poles are about to reverse – more often than not the field recovers its original structure, and this waning-recovering event is known as a geomagnetic excursion.
The researchers modeled the geomagnetic field between 30,000 and 50,000 years ago. Their aim was to examine the two most recent geomagnetic excursions – the Lascamp, which occurred around 41,000 years ago, and Mono Lake, which occurred around 34,000 years ago. The team found that the magnetic field at those times looked nothing like it does today, indicating that the current changes aren't warning signs of any impending excursion or reversal.
"There has been speculation that we are about to experience a magnetic polar reversal or excursion," says Richard Holme, co-author of the study. "However, by studying the two most recent excursion events, we show that neither bear resemblance to current changes in the geomagnetic field and therefore it is probably unlikely that such an event is about to happen. Our research suggests instead that the current weakened field will recover without such an extreme event, and therefore is unlikely to reverse."
To back it up, the team also found two periods where the field's structure was most similar to how it is today: 49,000 and 46,000 years ago. The field at these times had "anomalies" similar to – but much stronger than – that over the South Atlantic today, and yet neither developed into anything. Studies of chlorine and beryllium isotopes indicate that more cosmic radiation was indeed reaching the surface 46,000 years ago.
The results of this, as well as other similar studies, should help allay any fears of an impending pole reversal. Not only is it not likely to happen any time soon, but even if it did we don't have anything to worry about.
The research was published in the Proceedings of the National Academy of Sciences.
Source: University of Liverpool
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