Earth's magnetic field shifts ten times faster than expected

The Earth’s magnetic field can change direction up to ten times faster than previously realized, according to a new study from the University of Leeds and UC San Diego.

Satellites have improved efforts to  measure and track the ever-shifting magnetic field in recent years, but scientists also need to examine how the field has changed and evolved throughout history.

“We have very incomplete knowledge of our magnetic field prior to 400 years ago,” said study co-author Dr. Chris Davies. “Since these rapid changes represent some of the more extreme behavior of the liquid core they could give important information about the behavior of Earth’s deep interior.”

The magnetic field is generated by electric currents that flow in the planet’s molten core. The currents are hundreds of miles wide and pass through the crust into outer space. 

The field does not just help to guide navigation systems, but also protects the atmosphere from damaging solar winds and prevents extraterrestrial radiation from reaching the planet.

To measure the magnetic field back through geological time, experts typically analyze sediments, lava flows, and human-made artifacts. However, the rates of changes estimated through these types of studies are not necessarily accurate.

In the new study, the researchers tried out a different approach by combining computer simulations with a recently published reconstruction of time variations in Earth’s magnetic field spanning the last 100,000 years.

The most recent estimates report that the magnetic field changes up to one degree per year. However, the new study has revealed that directional variations in the Earth’s magnetic field have historically reached rates that are up to 10 times faster.

The research showed that such rapid changes are associated with local weakening of the magnetic field. According to study authors, this means that the changes have generally occurred around times when the field reversed polarity or when the dipole axis moved far from the locations of the North and South geographic poles.

For example, the experts pinpointed a sharp change in the geomagnetic field direction of roughly 2.5 degrees per year 39,000 years ago. The shift was associated with a weak field strength in a confined spatial region off the west coast of Central America.

The analysis indicates that the fastest directional changes are associated with reversed movement across the surface of the liquid core, primarily at lower latitudes.

“Understanding whether computer simulations of the magnetic field accurately reflect the physical behaviour of the geomagnetic field as inferred from geological records can be very challenging,” said study co-author Professor Catherine Constable.

“But in this case we have been able to show excellent agreement in both the rates of change and general location of the most extreme events across a range of computer simulations.”

“Further study of the evolving dynamics in these simulations offers a useful strategy for documenting how such rapid changes occur and whether they are also found during times of stable magnetic polarity like what we are experiencing today.”

The research is published in the journal Nature Communications.

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By Chrissy Sexton, Earth.com Staff Writer