A magnetic field record from ancient minerals for Iron Age southern Africa has been collected for the first time, and the findings suggest the region of Earth's core beneath southern Africa plays a crucial role in the phenomenon of pole reversal.
Reversals of the North and South Poles have occurred periodically throughout history, with the most recent likely to have taken place about 800,000 years ago, the University of Rochester reported. The findings suggest these fascinating reversals, which can take up to 15,000 years to complete, have generally originated in the core region beneath southern Africa.
"It has long been thought reversals start at random locations, but our study suggests this may not be the case," said geophysicist John Tarduno from the University of Rochester.
The team collected the data examined in the revealing study at five sites along South Africa's borders with Zimbabwe and Botswana. Today, this regions is characterized by an unusually weak magnetic field. Earth's magnetic field has declined by at least 16 percent since 1840, and some have speculated this means we are beginning to experience the next field reversal.
These new findings may explain the extremely low field strength in the analyzed region of Africa, known as a Large Low Shear Velocity Province (LLSVP). The top of the core in this area is overlain by hot, dense mantle rocks. It is believed to influence the direction of churning liquid iron that is known to disrupt the magnetic field, leading to a loss of magnetic intensity.
The clues to this stunning finding were found stored in minerals, such as magnetite. Knowledge ancient African practices, such as the cleansing of agricultural communities, lead to the study's conclusion. In the cleansing practice, huts and grain bins were burnt to the ground, causing the clay floors to reach temperatures close to 2,000 degrees Fahrenheit. These scorching temperature are hot enough to erase the magnetic information stored in nearby magnetite, and create a new record of the magnetic field.
Using this insight, the researcher determined there was a 30 percent drop in magnetic field intensity from 1225 to 1550 A.D. This suggests the process that caused the weakening may be recurring today.
"Because rock in the deep mantle moves less than a centimeter a year, we know the LLSVP is ancient, meaning it may be a longstanding site for the loss of magnetic field strength," Tarduno said. "And it is also possible that the region may actually be a trigger for magnetic pole reversals, which might happen if the weak field region becomes very large."
The findings were published in a recent edition of the journal Nature Communications.
