Lumps of clay excavated from the iron age grain bins in South Africa. Early farmers burned their huts of clay and grain storage buildings in times of drought as part of a purification ritual, unconsciously blocking the magnetic properties of the minerals in the clay in place.
(With Thanks To John Tarduno)
A valve in the magnetic field of the Earth may be brewing. And if it is, an electromagnetic blob deep beneath south Africa is probably ground zero for the change.
New research with the help of clay burned in cleansing rituals by iron age farmers found that over the past 1500 years, an electromagnetic anomaly in the Southern Hemisphere has waxed and waned, with the magnetic field in the region of weakening and strengthening. This strangeness may presage a gradual reversal of the magnetic field so that magnetic north shifts to the south pole and vice versa. (A flip-flop of this last kind occurred 780,000 years ago.)
The study suggests that the magnetic field under south Africa may not be funny today, study co-author John Tarduno, who researches the Earth’s magnetism at the University of Rochester in New York, told Science. It can be a long hotspot for changes in the global magnetic field.
“This may be the place where the reversal started, at least spending over the past millions of years,” Tarduno said. [7 Ways the Earth Changes in the Blink of an Eye]
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The planet of the magnetic field is generated by the churning of the liquid iron in the core. Without the field, life on the planet would be much different, if not impossible: This invisible shield protects the earth’s surface from deadly cosmic radiation.
Now, the field is undergoing a weakening, and no one knows for sure why. The South Atlantic Anomaly, a region of the magnetic field that extends from South-Africa, Chile, is particularly weak, Tarduno said, so scientists have become interested in figuring out what would be in the core under that area.
The problem is that for about 160 years or so ago, with the advent of magnetic observatories and (eventually) satellite observations, there were not many records of what the magnetic field looked like in the Southern Hemisphere, Tarduno said. Ninety percent of the data that there are, comes from the northern half of the planet. To start with the remedy that inequality, Tarduno and his team excavated clay from the Limpopo River Valley of Zimbabwe, South Africa and Botswana. In times of drought, hundreds to thousands of years ago, Bantu-speaking farmers burn their huts of clay and grain bins in ritual ceremonies. Who knows these old farmers, the fire heat the magnetic minerals in the clayand locked in place a record of the strength and the orientation of the field at that time. Now the researchers in the study of those properties to find out what the magnetic field was doing at that moment in time.
Locked up in clay
The excavations revealed these burnt clay so long ago as A. D. 425, Tarduno said, providing the longest record yet of the magnetic field in south Africa. The data show that the magnetic field, sudden directional shifts between A. D. 400 and 450, and then again between A. D. 750 and 800. Between about A. D. 1225 and 1550, the field is significantly weakened. The first two teams may also indicate a weakened field, Tarduno said, but more research is needed to determine the magnetic intensity in those time frames. The researchers reported their findings Feb. 15 in the journal Geophysical Research Letters.
What these shifts suggest is that what happens in the Southern Hemisphere of the magnetic field of today can happened, Tarduno said.
The field shifts may have to do with underlying processes churning deep below the surface of the Earth, Tarduno said. In recent years, scientists have documented a strange patch of magnetic field below south Africa, on the border between the core and the mantle, where the polarity of the field is reversed.
“That patch may be largely responsible for the declining magnetic field,” Tarduno said.
The patch is like an eddy in a stream, ” he said. For what the causes of the eddy, it can be something odd on the mantle right above the core in that location, ” he said. The mantle below south Africa is unusual, and possibly both hotter and denser than the surrounding mantle, ” he said.
“We think that the cause is that there are changes in the flow of the iron [core] as it is in this region,” Tarduno said.
That could mean that south Africa is the origin for the magnetic field reversals, Tarduno said, but there is no guarantee that the field flip-now — the weakening can also disappear, as in previous centuries.
Even if the area is not backwards, but the weakening could societal implications, Tarduno said.
“These are not of the nature of the disaster movies. That’s not the point,” he said. Instead, a weakening of the field could let in more cosmic rays hit the Earth, causing the infrastructure, such as the power grid more susceptible to geomagnetic storms, and even the changing of the atmospheric chemistry, so there are more UV rays can sneak through, causing an increased risk of skin cancer in humans.
“It is definitely something that we need to keep an eye on,” Tarduno said.
Original article on Live Science.