The intensity of Earth’s magnetic field has been dropping for the last two centuries, at a rate that some researchers suspect may cause the field to bottom out in few millennia. A new study of recent magnetic field near-reversals has found it is unlikely that such an event will take place anytime soon.
Earth’s magnetic field connects the North Pole (orange lines) with the South Pole (blue lines) in this NASA-created image. Image credit: NASA’s Goddard Space Flight Center.
Earth’s magnetic field is generated in the planet’s liquid iron outer core and protects the surface from harmful solar radiation. It also aids in human navigation, animal migrations and protects telecommunication and satellite systems.
The strength and structure of the geomagnetic field has varied at different times throughout geological history.
At certain periods, the field has weakened to such an extent that it was able to swap the positions of magnetic north and magnetic south, whilst geographic north and geographic south remain the same.
Called a geomagnetic reversal, the last time this happened was 780,000 years ago.
However, geomagnetic excursions, where the field comes close to reversing but recovers its original structure, have occurred more recently.
In a paper published in the Proceedings of the National Academy of Sciences, University of Liverpool’s Professor Richard Holmes and co-authors model observations of the geomagnetic field of the two most recent geomagnetic excursion events:
(i) the Laschamp, approximately 41,000 years ago;
(ii) Mono Lake, around 34,000 years ago, where the field came close to reversing but recovered its original structure.
The team’s model reveals a field structures comparable to the current geomagnetic field at both approximately 49,000 and 46,000 years ago, with an intensity structure similar to, but much stronger than the so-called South Atlantic Anomaly (SAA), which stretches from Chile to Zimbabwe; their timing and severity is confirmed by records of cosmogenic nuclides.
However, neither of these SAA-like fields developed into an excursion or reversal.
“There has been speculation that we are about to experience a magnetic polar reversal or excursion,” Professor Holmes said.
“However, by studying the two most recent excursion events, we show that neither bear resemblance to current changes in the geomagnetic field and therefore it is probably unlikely that such an event is about to happen.”
“Our research suggests instead that the current weakened field will recover without such an extreme event, and therefore is unlikely to reverse.”
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Maxwell Brown et al. Earth’s magnetic field is probably not reversing. PNAS, published online April 30, 2018; doi: 10.1073/pnas.1722110115
