Geomagnetic reversal dating
You might imagine the magnetic field is a timeless, constant aspect of life on Earth, and to some extent you would be right. Every so often – on the order of several hundred thousand years or so – the magnetic field has flipped. And when the field flips it also tends to become very weak.
What currently has geophysicists like us abuzz is the realization that the strength of Earth’s magnetic field has been decreasing for the last 160 years at an alarming rate.
The communities often responded to times of drought with rituals of cleansing that involved burning mud granaries.
This somewhat tragic series of events for these people was ultimately a boon many hundreds of years later for archaeomagnetism.
Each floor is a small magnetic observatory, with its compass frozen in time immediately after burning.
With our colleagues, we’ve focused our sampling on Iron Age village sites that dot the Limpopo River Valley, bordered today by Zimbabwe to the north, Botswana to the west and South Africa to the south. What we found reveals a period in the past, near A. 1300, when the field in that area was decreasing as rapidly as it is today.
Just as in the case of the firing and cooling of a pot, the clay in these structures recorded Earth’s magnetic field as they cooled.
And because more radiation would reach Earth’s surface under very low field strengths during a global reversal, it also might affect rates of cancer.
The Conversation UK receives funding from Hefce, Hefcw, SAGE, SFC, RCUK, The Nuffield Foundation, The Ogden Trust, The Royal Society, The Wellcome Trust, Esmée Fairbairn Foundation and The Alliance for Useful Evidence, as well as sixty five university members.
View the full list The Earth is blanketed by a magnetic field.
This collapse is centered in a huge expanse of the Southern Hemisphere, extending from Zimbabwe to Chile, known as the South Atlantic Anomaly.
The magnetic field strength is so weak there that it’s a hazard for satellites that orbit above the region – the field no longer protects them from radiation which interferes with satellite electronics.Upon cooling, the magnetic minerals record the direction and intensity of the magnetic field at that time.