In 2022, a group of scientists unveiled a haunting soundtrack at Solbjerg Square in Copenhagen. They had converted Earth’s magnetic signals from 32 locations into sound to highlight the planet’s magnetic field, the invisible shield against harmful cosmic radiation, and its fluctuations over the past 100,000 years.
Two years later came another soundtrack, but this was no ordinary hum. It captured Laschamps, an extreme geomagnetic excursion that occurred 41,000 years ago, during which the Earth’s magnetic field weakened to just 5 per cent of its current strength. The excursion saw the magnetic north and south poles briefly switch places. The soundtrack, available on the European Space Agency’s website, has an eerie, alien-like quality. The project is based on research by Sanja Panovska of the GFZ German Research Centre for Geosciences in Potsdam, and her colleagues. Now, the team is working on another composition, recreating the Brunhes-Matuyama reversal, a far more extreme event that took place 780,000 years ago. “If the Earth retains the change in polarity for more than 100,000 years, scientists label them as reversals. Otherwise, they are excursions,” says Mamilla Venkateshwaralu, senior principal scientist at the National Geophysical Research Institute, Hyderabad, under the Council of Scientific and Industrial Research. The soundtrack is expected later this year. “It is going to sound different from the excursion event,” says Panovska.
Among its many roles, Earth also functions as a giant magnet, with magnetic field lines stretching from the north to the south magnetic pole. It originates 2,900 km below our feet in the liquid outer core, sandwiched between the mantle and the solid inner core, and is powered by electric currents generated by the movement of molten iron. Extending outward, it forms a protective bubble.
Much about the magnetic field, though, remains a mystery, including what drives reversals and excursions. One known fact is that it fluctuates over time due to the moving fluid in the outer core, which is powered by heat release from the inner core and the rotation of the planet. “If the flow is clockwise, we have normal polarity. If it moves 180° to anticlockwise direction, we get a reversal in polarity,” says Venkateshwarlu. Over the past 200 years, its strength has weakened by 10 per cent. If this decline continues at the current rate, models suggest the magnetic field could drop to zero in about 1,500-1,600 years, raising questions about whether we are heading towards another reversal or excursion. Data from the US National Aeronautics and Space Administration (NASA) show that over the last 83 million years, Earth’s magnetic poles have reversed 183 times.
Excursions are far more frequent, occurring 10 times as often. Since Brunhes-Matuyama, the most recent reversal, the planet has experienced three significant excursions: the Norwegian-Greenland Sea event (64,500 years ago), Laschamps and Mono Lake (34,500 years ago). “It is difficult to predict reversals or excursions because they occur without any periodicity,” says William Brown, a geophysicist in the geomagnetism team of the British Geological Survey.
The impact of these events also remains inconclusive. A 2021 study published in Science concluded that Laschamps caused substantial changes in atmospheric ozone concentration, impacting the climate over the mid to high latitudes in both hemispheres. The study noted that climatic shifts and extinction phases overlapped with the event, suggesting a link. But Panovska’s yet-to-be-published study on Laschamps’ impact on Neanderthals produced contrasting results. “We found no evidence suggesting that the event affected life on Earth. The reason is that we have an atmosphere, which offers protection against cosmic rays,” she says. A 2019 study in Science Advances estimates the Brunhes-Matuyama reversal took at least 22,000 years to complete, suggesting that society would have generations to adapt to a future magnetic instability.
Another mystery is the drifting north magnetic pole. First recorded in 1831 in the Canadian Arctic, it has since moved over 1,100 km towards Siberia, accelerating from 16 km per year in the 1990s to 35 km per year today. Meanwhile, the magnetic south pole has remained relatively stable, shifting just 5 km per year. “The differing behaviour of the north and south poles reflects processes in the outer core. It is likely due to turbulence in the flow, but we still do not fully understand why it speeds or slows down,” says Brown.
Despite many unknowns, scientists are making strides in understanding the Earth’s magnetic behaviour. “As computers become more advanced, we can better represent how the magnetic field is generated and the dynamics driving these changes,” says Brown. Researchers rely on geomagnetic observatories and satellites to study the magnetic field. Together, these sources offer a comprehensive picture of how the field is evolving over time.
But geomagnetic observatories have only been operational for about a century and satellite data have been available for just a few decades. To understand the magnetic field over longer timescales, scientists analyse ship logs dating back to 1590, which recorded compass directions.
Yet, ship logs alone do not provide a complete geological history. To fill this gap, scientists turn to geological and archaeological evidence, collecting samples from volcanic regions, lakes, oceans and archaeological sites. Lava-formed rocks, ocean and lake sediments, and ancient pottery all preserve signatures of the geomagnetic field at the time of their formation. “When the field is stronger, more grains align in the sediment, leading to stronger magnetisation,” says Bruce Buffett, professor at the University of California, Berkeley. Using geological samples, Venkateshwaralu and his team recently found traces of excursion events in Uttarakhand, including the Bagwalipokar excursion events 15,500-14,700 years ago and 8,000-2,850 years ago.
In a 2023 study in JGR Space Physics, Panovska and colleagues examined cosmogenic isotopes, such as beryllium-10 and carbon-14, found in ice cores and sediments. Their analysis showed that during the Laschamps excursion, global beryllium-10 production more than dou-bled. These isotopes form from the reaction of cosmic rays with oxygen and nitrogen atoms in the atmosphere, which then get deposited on land, ice and sea during precipitation. The idea is that more cosmic rays get deflected when the magnetic field is strong, and fewer cosmic isotopes form as a result. But when the field is strong, less cosmogenic isotopes are produced.
Scientists also speculate that geomagnetic reversals and excursions may be linked to the South Atlantic Anomaly (SAA), a region spanning South America and South Africa where the Earth’s magnetic field is weakest. SAA allows cosmic rays and charged particles to penetrate into the atmosphere, exposing spacecraft in low Earth orbit to harmful radiation. However, a 2018 study published in the Proceedings of the National Academy of Sciences found no evidence linking SAA to reversals. “In the last hundred thousand years, features like SAA formed six to nine times. The field strength has recovered in the past. So we think the current magnetic field is probably not going to reverse soon,” says Richard Holme, professor of Geomagnetism, University of Liverpool, and one of the authors of the report.
While scientists cannot yet predict geomagnetic reversals or excursions far into the future, they can forecast the magnetic field’s behaviour up to five years ahead. In December 2024, the US National Geospatial-Intelligence Agency and the UK’s Defence Geographic Centre released an updated World Magnetic Model, used by military and civilian navigation systems. “To make predictions, we analyse recent measurements and extrapolate trends forward,” says Brown. Scientists are optimistic that future advancements in computational resources will enable higher-resolution models, bringing us closer to understanding and forecasting the planet’s magnetic behaviour.
This article was originally published in the April 1-15, 2025 print edition of Down To Earth