A new ‘Out of Africa’ theory explains why Earth’s magnetic poles may soon switch

The strength of Earth’s magnetic field has been decreasing for the last 160 years. It’s happening in a patch centered in a huge expanse extending from Zimbabwe to Chile, known as the South Atlantic Anomaly.

There’s a patch of reversed polarity beneath southern Africa at the core-mantle boundary where the liquid iron outer core meets the slightly stiffer part of the Earth’s interior. In this area, the polarity of the field is opposite to the average global magnetic field.

Location of the South Atlantic Anomaly. Michael Osadicw/John Tarduno, CC BY-ND

Earth has a protective layer that shields all life from hazardous solar radiation—the magnetic field.

The magnetic field is basically that which makes compasses point north and helps our atmosphere against charged particles originating from space.

If Earth did not have a magnetic field, our atmosphere would slowly be stripped away by radiation, and life would eventually cease to exist on our planet.

Something similar occurred on Mars.

According to scientists, the slow destruction of our neighbor’s planet atmosphere was caused by “huge rope-like tendrils of magnetic rotations”. The red planet’s once hospitable atmosphere was blown away in the distant past because Mars’ magnetic field shut down. NASA scientists say that even though the red planet had a magnetic field, around 4.2 billion years ago it vanished.

This means that when Mars was much younger, it was much warmer and wetter, meaning that it was a very good candidate for life to develop. Scientists believe that Mars’ oceans evaporated due to the planet’s thinning atmosphere which caused it to leak into space.

If Earth’s magnetic field was lost, the same thing could happen on Earth. However, in time Earth’s magnetic field changes and every once in a while—during a period of several hundred years or so— the magnetic field switches. North points to the south and vice versa. During the time the field flips, it tends to become weak.

Scientists note that the strength of Earth’s magnetic field has been decreasing in the last 160 years at an ALARMING rate. This collapse is centered in a huge expanse of the Southern Hemisphere, extending from Zimbabwe to Chile, known as the South Atlantic Anomaly.

Curiously, the magnetic field strength is so weak that it poses a risk for satellites that orbit above the region since the field is unable to protect spacecraft from radiation, which even interferes with satellite electronics.

Scientists want that the field is continuing to weaken, which points to the possibility of greater problems, including a GLOBAL REVERSAL of the magnetic field.

To understand the issue more precisely, scientists are turning to some perhaps unexpected data sources, including 700-year-old African archaeological records, to figure it out.

Cutaway image of the Earth’s interior. Kelvinsong, CC BY-SA

Scientists explain that our planet’s magnetic field is created by convecting iron in our planet’s liquid outer core.

Thanks to the various sources of observatory and satellite data that document the magnetic field of recent times, scientists are able to create models of what the magnetic field may look like if we positioned a compass just above our planet’s swirling liquid iron core.

As detailed in The Conversation, scientists state that it reveals an astonishing detail: There’s a patch of reversed polarity beneath southern Africa at the core-mantle boundary where the liquid iron outer core meets the slightly stiffer part of the Earth’s interior. In this area, the polarity of the field is opposite to the average global magnetic field. If we were able to use a compass deep under southern Africa, we would see that in this unusual patch north actually points south.

It is precisely this patch which is believed to be one of the main culprits of the South Atlantic Anomaly.

As noted in previous studies, our planet’s poles have reversed quite a few times over the history of the planet, the last reversal is in the distant past, some 780,000 years ago.

However, the rapid rate at which the magnetic field is currently decaying raises question of what was happening prior to the last 160 years.

This is where Archaeomagnetism can help

Archaeomagnetism is the field where geophysicists team with archaeologists to learn about the past magnetic field. How is this done? In ancient times, the clay used to make pottery naturally cantinas small amount of magnetic minerals like magnetite.

When the ancients heated the clay to make the pot, magnetic minerals lose any magnetism they may have help. When the material cools down, the magnetic minerals record the direction and intensity of the magnetic field at the time when the pot was built.

If experts are able to determine the age of the pot, or if they know from which archaeological site it originated, with the aid or radiocarbon dating, then the pot’s archaeomagnetic history can be recovered.

Why is this important? Well, the Southern Hemisphere archaeomagnetic record is scant, but there have been virtually no data from southern Africa—precisely the place where experts can learn a LOT about the reversed core patch creating today’s South Atlantic Anomaly.

Interestingly, there’s hope thanks to the ancestors of today’s Africans, the Bantu-speaking metallurgists and farmers who began to migrate into the region between 2,000 and 1,500 years ago.

As it turns out, these Iron Age people lived in huts which were built of clay.

This has allowed scientists to sample them to obtain a record of both the direction and strength of their contemporary magnetic field.

First results revealed a period in the past, near A.D. 1300, when the field in that area was decreasing as rapidly as it is today. Later the intensity increased however at a much slower rate.

According to scientists, the existence of two intervals of rapid magnetic field decay—the one that occurred some 700 years ago and the current one— indicates we are looking at a recurring phenomenon.

As noted in The Conversation, scientists speculate that these reversed core patches grow rapidly and then wane more slowly. Occasionally one patch may grow large enough to dominate the magnetic field of the Southern Hemisphere – and the poles reverse.

Experts conclude:

“The conventional idea of reversals is that they can start anywhere in the core. Our conceptual model suggests there may be special places at the core-mantle boundary that promote reversals. We do not yet know if the current field is going to reverse in the next few thousand years, or simply continue to weaken over the next couple of centuries.”

“But the clues provided by the ancestors of modern-day southern Africans will undoubtedly help us to further develop our proposed mechanism for reversals. If correct, pole reversals may be “Out of Africa.”

Source, reference, and additional reading material:

Vincent HarePostdoctoral Associate in Earth and Environmental Sciences, University of Rochester

John TardunoProfessor of Geophysics, University of Rochester

The Conversation: Does an anomaly in the Earth’s magnetic field portend a coming pole reversal?

Featured image credit: Berkeley Lab News Center – Lawrence Berkeley National Laboratory

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