When Earth鈥檚 magnetic field will flip remains uncertain (Image: G. Glatzmaier, Los Alamos National Laboratory/ P. Roberts, UCLA/ SPL)
Flipping heck! Deposits from fires set by farmers centuries ago reveal that Earth鈥檚 magnetic field dramatically weakened in the past without actually flipping 鈥� suggesting that current field weakening might not necessarily lead to a pole swap either.
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Earth鈥檚 poles have swapped in the past, but without a regular pattern, says of the University of Rochester in New York. This means we don鈥檛 know when they will flip again 鈥� but many suspect it might be soon: the field has been weakening since about 1840. A flip may affect our power grids and communications systems.
Cottrell鈥檚 team examined magnetic minerals that had their magnetism orientated when South Africa鈥檚 farmers lit fires between 500 and 1000 years ago.
This captures the size and direction of Earth鈥檚 magnetic field. 鈥淚t fixes the magnetic field at that time,鈥� says Cottrell.
The analysis shows that around the year 1370, field strength was falling by 0.054 microteslas a year 鈥� substantially faster than today鈥檚 drop of 0.036 microteslas.
Until now, we had a poor record of magnetic field changes in the southern hemisphere.
Journal reference: Nature Communications , DOI: 10.1038/ncomms8865
