Earth’s geomagnetic field, which scientists have been warning about for hundreds of years, is not going to suddenly flip, according to a new study.
Now it looks like the magnetic N Pole will remain in the north and the magnetic South Pole will remain in the south – for at least a few thousand years or so.
“In terms of geologic time, we are currently in a period of a very strong geomagnetic field,” geologist Andreas Nilsson of Lund University in Sweden said in an email. “Therefore, there is a long way to go before the polarity reversal.”
Nilsson is the lead author of a study published this month by the National Academy of Sciences that examined 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 been steadily weakening since the first geomagnetic observatories were established in the 1840s, while the SAA’s weakness has increased over that time.
This has led some scientists to theorize that the strength of the geomagnetic field decreases just before it reverses direction – something it has done several times in the past, according to layers of rock deposited over millions of years that show previous changes.
But a new study has shown that large geomagnetic anomalies occurred earlier and relatively recently in geologic time without causing a field reversal.
These anomalies usually disappear after a few hundred years – and there is no indication that the SAA will be any different, Nilsson said.
Nilsson and colleagues have studied how the Earth’s magnetic field has changed over the past 9,000 years by studying 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. According to Nilsson, the magnetite lost its orientation when it was heated during the firing process, and the grains became magnetized again by the geomagnetic field when they cooled, resulting in a record-breaking field strength.
The study shows that the current state of the Earth’s magnetic field is similar to the state around 600 BC, when two large weaknesses dominated the Pacific Ocean.
However, the anomalies over the Pacific disappeared within the next 1,000 years, and it is likely that the SAA will also disappear, Nilsson said — probably in about 300 years, leaving a stronger and more even geomagnetic field.
A geomagnetic reversal would probably not be a disaster, but it would certainly be inconvenient.
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 makes magnetic compasses work.
Geological studies have shown that in the last 2.6 million years alone, the geomagnetic field has reversed 10 times. The last time was about 780,000 years ago, an event known as the Brunhes-Matuyama reversal.
But although this process is related to movements in the molten core, it is not well understood – and scientists are not sure when the next reversal will occur.
“The Earth’s magnetic field changes on average every 300,000 to 400,000 years,” explained Adrian McWorthy, 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 were periods when it didn’t reverse until 30 million years ago, but we kind of should.”
Geological evidence from previous reversals shows that it can take 500 to 2,000 years for the Earth’s magnetic field to reverse direction, gradually getting weaker in the predominant direction and gradually stronger in the opposite direction, he says.
Mcworthy notes that while modern navigation systems such as the Global Positioning System (GPS) now rely on orbiting satellites, the navigation satellites themselves still rely on the geomagnetic field for their orientation.
It’s also likely that satellites in low orbits, which are currently being projected by the Earth’s magnetic field, could be damaged by large amounts of solar radiation during a field reversal, though they could be protected by making them heavier, he said.
At its weakest, the geomagnetic field would be about 20 percent of what it is now, he said, leading to an increase in solar radiation on the surface for a while, though probably not enough to affect life there.
However, one curious side effect of a complete field reversal would be that the spectacular auroras that now occur mostly over the poles would be observed across the globe.
“It would actually be pretty exciting,” Maxworthy said. “Just like we’re getting the northern and southern lights now, we’ll see them at all latitudes, including over the equator.”
Nilsson cautions that while his study of the South Atlantic Anomaly suggests that it will disappear without issue in a few hundred years, there is still a possibility that the Earth’s magnetic field will start to change anyway, although scientists see no signs that it will happen.
But “we can definitely be wrong,” he said.
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