Above our heads, something is not right. Earth's magnetic field is in a state of dramatic weakening - and according to mind-boggling new research, this phenomenal disruption is part of a pattern lasting for over 1,000 years.
Earth's magnetic field doesn't just give us our north and south poles; it's also what protects us from solar winds and cosmic radiation - but this invisible force field is rapidly weakening, to the point scientists think it could actually flip, with our magnetic poles reversing.
As crazy as that sounds, this actually does happen over vast stretches of time. The last time it occurred was about 780,000 years ago, although it got close again around 40,000 years back. When it takes place, it's not quick, with the polarity reversal slowly occurring over thousands of years.
Nobody knows for sure if another such flip is imminent, and one of the reasons for that is a lack of hard data.
The South Atlantic Anomaly
The region that concerns scientists the most at the moment is called the South Atlantic Anomaly - a huge expanse of the field stretching from Chile to Zimbabwe.
Read also: What is the South Atlantic Anomaly?
The field is so weak within the anomaly that it's hazardous for Earth's satellites to enter it, because the additional radiation it's letting through could disrupt their electronics.
The South Atlantic Anomaly (SAA) is an area where Earth's inner Van Allen radiation belt comes closest to Earth's surface, dipping down to an altitude of 200 kilometers (120 mi). The shape of the SAA changes over time. Since its initial discovery in 1958, the southern limits of the SAA have remained roughly constant while a long-term expansion has been measured to the northwest, the north, the northeast, and the east.
At an altitude of approximately 500 km (310 mi), the SAA spans from −50° to 0° geographic latitude and from −90° to +40° longitude. The highest intensity portion of the SAA drifts to the west at a speed of about 0.3° per year, and is noticeable in the references listed below. The drift rate of the SAA is very close to the rotation differential between the Earth's core and its surface, estimated to be between 0.3° and 0.5° per year.
Magnetic field intensity at Earth's surface in 2014 (top) and 2025 (bottom), as measured by ESA's SWARM spacecraft.
The International Space Station, orbiting with an inclination of 51.6°, requires extra shielding to deal with this problem. The PAMELA experiment, while passing through the SAA, detected antiproton levels that were orders of magnitude higher than expected.
Read also: Theories on Underwater Anomalies
The SAA is believed to have started a series of events leading to the destruction of the Hitomi, Japan's most powerful X-ray observatory.
The Quest for Archeomagnetic Data
"We've known for quite some time that the magnetic field has been changing, but we didn't really know if this was unusual for this region on a longer timescale, or whether it was normal," says physicist Vincent Hare from the University of Rochester in New York.
One of the reasons scientists don't know much about the magnetic history of this region of Earth is it lacks what's called archeomagnetic data - physical evidence of magnetism in Earth's past, preserved in archaeological relics from bygone ages.
One such bygone age belonged to a group of ancient Africans, who lived in the Limpopo River Valley - which borders Zimbabwe, South Africa, and Botswana: regions that fall within the South Atlantic Anomaly of today.
Approximately 1,000 years ago, these Bantu peoples observed an elaborate, superstitious ritual in times of environmental hardship. During times of drought, they would burn down their clay huts and grain bins, in a sacred cleansing rite to make the rains come again - never knowing they were performing a kind of preparatory scientific fieldwork for researchers centuries later.
Read also: Off the Coast of Africa
"When you burn clay at very high temperatures, you actually stabilise the magnetic minerals, and when they cool from these very high temperatures, they lock in a record of the earth's magnetic field," one of the team, geophysicist John Tarduno explains.
As such, an analysis of the ancient artefacts that survived these burnings reveals much more than just the cultural practices of the ancestors of today's southern Africans.
The researchers gathered data for this project from an unlikely source: ancient clay remnants from southern Africa dating back to the early and late Iron Ages. The Rochester team, which included several undergraduate students, collaborated with archaeologist Thomas Huffman of the University of Witwatersrand in South Africa, a leading expert on Iron Age southern Africa.
During the Iron Age in southern Africa, around the time of the first millennium, there was a group of Bantu-speaking people who cultivated grain and lived in villages composed of grain bins, huts, and cattle enclosures. Droughts were devastating to their agriculturally based culture.
Researchers excavate the samples, orient them in the field, and bring them back to the lab to conduct measurements using magnetometers.
Recurrent Anomalies: A Glimpse into the Past
"We were looking for recurrent behavior of anomalies because we think that's what is happening today and causing the South Atlantic Anomaly," Tarduno says.
"We found evidence that these anomalies have happened in the past, and this helps us contextualise the current changes in the magnetic field."
Like a "compass frozen in time immediately after [the] burning", the artefacts revealed that the weakening in the South Atlantic Anomaly isn't a standalone phenomenon of history. Similar fluctuations occurred in the years 400-450 CE, 700-750 CE, and 1225-1550 CE - and the fact that there's a pattern tells us that the position of the South Atlantic Anomaly isn't a geographic fluke.
“We were looking for recurrent behavior of anomalies because we think that’s what is happening today and causing the South Atlantic Anomaly,” Tarduno says. The researchers discovered that the magnetic field in the region fluctuated from 400-450 AD, from 700-750 AD, and again from 1225-1550 AD.
Table: Historical Fluctuations in Earth's Magnetic Field
| Time Period | Event |
|---|---|
| 400-450 CE | Fluctuation in magnetic field |
| 700-750 CE | Fluctuation in magnetic field |
| 1225-1550 CE | Fluctuation in magnetic field |
The African Large Low Shear Velocity Province
"We're getting stronger evidence that there's something unusual about the core-mantel boundary under Africa that could be having an important impact on the global magnetic field," Tarduno says.
The current weakening in Earth's magnetic field - which has been taking place for the last 160 years or so - is thought to be caused by a vast reservoir of dense rock called the African Large Low Shear Velocity Province, which sits about 2,900 kilometres (1,800 miles) below the African continent.
"It is a profound feature that must be tens of millions of years old," the researchers explained in The Conversation last year. "While thousands of kilometres across, its boundaries are sharp."
The magnetic field is generated by swirling, liquid iron in Earth’s outer core. Seismological data has revealed a denser region deep beneath southern Africa called the African Large Low Shear Velocity Province. The region is located right above the boundary between the hot liquid outer core and the stiffer, cooler mantle.
This dense region, existing in between the hot liquid iron of Earth's outer core and the stiffer, cooler mantle, is suggested to somehow be disturbing the iron that helps generate Earth's magnetic field.
There's a lot more research to do before we know more about what's going on here.
Implications of a Weakening Magnetic Field
A major change in the magnetic field would have wide-reaching ramifications; the magnetic field stimulates currents in anything with long wires, including the electrical grid. Changes in the magnetic field could therefore cause electrical grid failures, navigation system malfunctions, and satellite breakdowns.
Even if a complete pole reversal is not in the near future, however, the weakening of the magnetic field strength is intriguing to scientists, Tarduno says.
As the researchers explain, the conventional idea of pole reversals is that they can start anywhere in the core - but the latest findings suggest what happens in the magnetic field above us is tied to phenomena at special places in the core-mantle boundary.
“We now know this unusual behavior has occurred at least a couple of times before the past 160 years, and is part of a bigger long-term pattern,” Hare says.
If they're right, a big piece of the field weakening puzzle just fell in our lap - thanks to a clay-burning ritual a millennia ago.
Structural irregularities in the magnetic field in the South Atlantic region - Yael Engbers
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tags: #Africa
