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Earth’s magnetic poles are (probably) not about to shift, scientists say

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Earth’s geomagnetic field, which scientists have been warning about for hundreds of years, isn’t about to flip suddenly after all, according to a new study.

It now looks like the magnetic north pole will stay in the north and the magnetic south pole will stay in the south – at least for a few thousand years or so.

“From the perspective of geologic time, we are currently in a period of very strong geomagnetic field,” geoscientist Andreas Nilsson of Sweden’s Lund University said in an email. “There is therefore a long way to go before a reversal of polarity.”

Nilsson is the lead author of research published this month by the National Academy of Sciences that studied a large weakness in the geomagnetic field known as the South Atlantic Anomaly, or SAA.

The study notes that the Earth’s magnetic field has steadily weakened since the first geomagnetic observatories were established in the 1840s, while the SAA’s weakness has increased over this period.

This has led some scientists to theorize that the geomagnetic field decreases in intensity just before it completely reverses direction – which it has done several times in the past, according to layers of rock deposited over millions of years that show previous reversals.

But the new research found that large geomagnetic anomalies have occurred before, and relatively recently in geologic time, without causing a field reversal.

These anomalies usually disappear a few hundred years later — and there is no indication that SAA will be any different, Nilsson said.

Nilsson and his colleagues studied how the Earth’s magnetic field has changed over the past 9,000 years by examining iron in volcanic rocks, ocean sediments and, in some cases, burnt archaeological artifacts.

These include clay pots fired in ancient kilns thousands of years ago, which sometimes contain small amounts of an iron ore called magnetite. The magnetite lost its alignment when heated in the firing process, and the grains became magnetized again by the geomagnetic field as they cooled, resulting in a record of the strength of the field, a Nilsson said.

The study shows that the current state of Earth’s magnetic field is similar to that of around 600 BC, when it was dominated by two large weaknesses over the Pacific Ocean.

Anomalies over the Pacific, however, faded over the next 1,000 years, and it’s likely the SAA will as well, Nilsson said — likely in about 300 years, leaving a stronger and more geomagnetic field. uniform.

A reversal of the geomagnetic field would probably not be catastrophic, but it would certainly be troublesome.

Scientists believe the field is generated by the flow of molten iron in the Earth’s core, about 1,800 miles below the surface. It acts as a shield against deadly solar radiation and also powers magnetic compasses.

Geological studies have shown that the geomagnetic field has reversed 10 times in the last 2.6 million years alone. The last time was around 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 is not well understood – and scientists do not know when the next reversal will occur.

“The Earth’s magnetic field reverses on average every 300 to 400,000 years,” said Adrian Muxworthy, professor of terrestrial and planetary magnetism at Imperial College London, who was not involved in the study. “But it’s chaotic. It’s not regular. There have been times when it hasn’t reversed for up to 30 million years, but we’re kind of due to one.

Geological records of previous reversals show that it can take 500 to 2,000 years for the Earth’s magnetic field to fully reverse becoming progressively weaker in the prevailing direction and progressively stronger in the opposite direction, he said. declared.

Muxworthy notes that while modern navigation systems, such as the Global Positioning System (GPS), now rely on orbiting satellites, the navigation satellites themselves still depend on the geomagnetic field for their alignments.

It is also likely that low-orbiting satellites that are currently being thrown around by the Earth’s magnetic field could be damaged by greater amounts of solar radiation during a field reversal, although they could be shielded by making them heavier. , did he declare.

At its weakest, the geomagnetic field would be around 20% of what it is now, which would lead to increased solar radiation at the surface for some time, although probably not enough to affect life there, a- he declared.

A curious side effect of a full field reversal, however, would be that the spectacular auroras that currently occur mostly over the poles would occur all over the world.

“It would actually be pretty exciting,” Muxworthy said. “Just as we now get the northern and southern lights, we would see them at all latitudes, including over the equator.”

Nilsson warns that while his study of the South Atlantic Anomaly suggests it will disappear safely in a few hundred years, there is always the possibility that Earth’s magnetic field will begin to reverse anyway, although the scientists see no signs that this will be the case.

But “we could certainly be wrong,” he said.