From Science Alert and U Rochester: “Mysterious Anomaly Under Africa Is Weakening Earth’s Magnetic Field”

ScienceAlert

From Science Alert

27 DEC 2018
PETER DOCKRILL

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(NASA Hubble Space Telescope/Flickr)

Above our heads, something is not right. Earth’s magnetic field is in a state of dramatic weakening – and according to mind-boggling research from earlier this year, 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 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. 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.

“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,” physicist Vincent Hare from the University of Rochester in New York said in February this year.

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.

“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 explained.

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.

“We were looking for recurrent behaviour of anomalies because we think that’s what is happening today and causing the South Atlantic Anomaly,” Tarduno said.

“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’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.”

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 better understand what’s going on here.

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.

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. What this all means for the future, though, no-one is certain.

“We now know this unusual behaviour has occurred at least a couple of times before the past 160 years, and is part of a bigger long-term pattern,” Hare said.

“However, it’s simply too early to say for certain whether this behaviour will lead to a full pole reversal.”

The findings are reported in Geophysical Review Letters.

See the full Science Alert article here .

From U Rochester: “Earth’s magnetic field fluctuations explained by new data”

February 27, 2018

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Earth’s geomagnetic field surrounds and protects our planet from harmful space radiation. (CC BY-SA 2.0 photo / Flickr user NASA Goddard Space Flight Center)

Using new data gathered from sites in southern Africa, University of Rochester researchers have extended their record of Earth’s magnetic field back thousands of years to the first millennium.

The record provides historical context to help explain recent, ongoing changes in the magnetic field, most prominently in an area in the Southern Hemisphere known as the South Atlantic Anomaly.

“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 Vincent Hare, who recently completed a postdoctoral associate appointment in the Department of Earth and Environmental Sciences (EES) at the University of Rochester, and is lead author of a paper published in Geophysical Research Letters [link is above].

Weakening magnetic field a recurrent anomaly

The new data also provides more evidence that a region in southern Africa may play a unique role in magnetic pole reversals.

he magnetic field that surrounds Earth not only dictates whether a compass needle points north or south, but also protects the planet from harmful radiation from space. Nearly 800,000 years ago, the poles were switched: north pointed south and vice versa. The poles have never completely reversed since, but for the past 160 years, the strength of the magnetic field has been decreasing at an alarming rate. The region where it is weakest, and continuing to weaken, is a large area stretching from Chile to Zimbabwe called the South Atlantic Anomaly.

In order to put these relatively recent changes into historical perspective, Rochester researchers—led by John Tarduno, a professor and chair of EES—gathered data from sites in southern Africa, which is within the South Atlantic Anomaly, to compile a record of Earth’s magnetic field strength over many centuries. Data previously collected by Tarduno and Rory Cottrell, an EES research scientist, together with theoretical models developed by Eric Blackman, a professor of physics and astronomy at Rochester, suggest the core region beneath southern Africa may be the birthplace of recent and future pole reversals.

“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 contextualize the current changes in the magnetic field.”

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. This South Atlantic Anomaly, therefore, is the most recent display of a recurring phenomenon in Earth’s core beneath Africa that then affects the entire globe.

“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.

A pole reversal? Not yet, say researchers.

The magnetic field is generated by swirling, liquid iron in Earth’s outer core. It is here, roughly 1800 miles beneath the African continent, that a special feature exists. 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. Sitting on top of the liquid outer core, it may sink slightly, disturbing the flow of iron and ultimately affecting Earth’s 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. A weakening of the magnetic field might also mean more harmful radiation reaches Earth—and trigger an increase in the incidence of skin cancer.

Hare and Tarduno warn, however, that their data does not necessarily portend a complete pole reversal.

“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. “However, it’s simply too early to say for certain whether this behavior will lead to a full pole reversal.”

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. “The possibility of a continued decay in the strength of the magnetic field is a societal concern that merits continued study and monitoring.”

This study was funded by the US National Science Foundation.

See the full U Rochester article here .


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