Flipping heck! Deposits from fires set by farmers centuries ago reveal that Earth’s magnetic field dramatically weakened in the past without actually flipping – suggesting that current field weakening might not necessarily lead to a pole swap either.
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A team of scientists led by John Tarduno, a geophysicist from the University of Rochester, and composed by other researchers from Witwatersrand University and Kwa-Zulu Natal University of South Africa conducted a study regarding the Earth’s magnetic field.
Their data is groundbreaking in the field of earth sciences and geophysics because it suggests that pole reversals don’t begin in random locations as previously thought.
That part of Africa belongs to a region called the South Atlantic Anomaly that today has an unusually weak magnetic field strength. They turned to archaeologists for extra help. These communities have cleansing practices which include burning of farm huts and grain bins. While it seems like a rather unimportant event for geophysicists, this practice of igniting the village would have created a fire that reached over 1000 degrees Celsius as it consumed the clay floors of the structures.
One of the central findings is that the core beneath that region of Africa is covered by a dense and hot mantle rock that lies 1500 miles below the surface, has steep sides, and is 1864 miles across, about the distance from New York to Paris, according to the release. When that flow shifts, the magnetic intensity shifts, the release said. He added that it is also a possibility that the region could activate magnetic pole reversals that might occur if the weak field region becomes extremely large.
Tarduno and his colleagues discovered that from 1225 to 1550 A.D, there has been a 30 percent decrease in magnetic field intensity. This parallels what is happening today in the region, leading the researchers to the conclusion that this gradual weakening may reappear every few (thousand) years.
Schematic illustration of Earth’s magnetic field. Since 1940, the Earth’s magnetic field has been weakening by about 16 percent. It happens all the time!
Until now, we had a poor record of magnetic field changes in the southern hemisphere.
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The scientists collected the data from five sites along South Africa’s borders with Zimbabwe and Botswana, near the Limpopo River.
