The fiery demise of ancient huts in southern Africa 1,000 years ago left clues to understanding a bizarre weak spot in the Earth's magnetic field — and the role it plays in the magnetic poles' periodic reversals.
Patches of ground where huts were burned down in southern Africa contain a key mineral that recorded the magnetic field at the time of each ritual burning. Those mineral records teach researchers more about a weird, weak patch of Earth's magnetic field called the South Atlantic Anomaly and point the way toward a possible mechanism for sudden reversals of the field.
[...] "They had this ritualistic burning of villages," Tarduno told Space.com. "Particularly in times of drought, the conclusion would be that there might have been some offence in the village, so the solution was to have a burning down of the village." The process was intended to cleanse the village, their collaborator archaeologist Thomas Huffman, from Witwatersrand University in South Africa, said in the statement.
At the very least, it cleansed the ground: The burning villages would reach temperatures of over 1,800 degrees Fahrenheit (1,000 degrees Celsius), which would melt the magnetic compounds like magnetite in the clay floors. The magnetite would become remagnetized by the Earth's magnetic field at the precise instant it cooled, ready to be analyzed centuries later.
Interesting that an act of destruction would be the reason we can learn centuries later. It's reminiscent of how we can thank fire for preserving so many examples of Akkadian cuneiform, written on clay tablets and baked when their storage areas were burned.
(Score: 1) by jdavidb on Friday July 31 2015, @01:42AM
The magnetite would become remagnetized by the Earth's magnetic field at the precise instant it cooled
Wait, isn't cooling usually a gradual phenomenon?
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(Score: 1) by Bogsnoticus on Friday July 31 2015, @02:56AM
It is a gradual phenomenom, but everyone knows the instant something cools. Its the very instant you touch it to see how hot it is, and your finger doesn't end up smelling and sounding like frying bacon.
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(Score: 1, Insightful) by Anonymous Coward on Friday July 31 2015, @03:20AM
Gradual on your time scale - virtually instantaneous on a geological time scale. The magnetic field won't change significantly over the time it takes to cool.
(Score: 0) by Anonymous Coward on Friday July 31 2015, @07:51AM
They're referring to the moment it passes the Curie Point on the way down, see:
https://en.wikipedia.org/wiki/Curie_point [wikipedia.org]
And, yes, it is named after THOSE Curies! They did other things before the radioactivity craze.