Hear Earth’s Magnetic Field Flip 41,000 Years Ago

Around 41,000 years ago, Earth’s magnetic field underwent a dramatic reversal. Thanks to an inventive rendering of data gathered by the European Space Agency’s Swarm satellite mission, it is now possible to actually ‘hear’ this monumental disturbance.

By pairing satellite observations with evidence tracing the movement of magnetic field lines around Earth, geoscientists reconstructed the Laschamps event in sound, using organic effects including creaking timber and the impact of colliding rocks.

Revealed in 2024 by the Technical University of Denmark and the German Research Center for Geosciences, the resulting audio recording is a haunting, alien-sounding track unlike anything heard before.

Earth’s magnetic field and shifting magnetic poles

Produced by the churning liquid metals within Earth’s core, the planet’s magnetic field extends tens to hundreds of thousands of kilometres into space. It protects life by diverting solar particles that could otherwise strip away the atmosphere.

As the iron and nickel inside Earth move, its magnetic field changes too, which means that both the North and South magnetic poles are perpetually travelling. The official location of the magnetic North Pole was recently updated as it continues moving away from Canada and towards Siberia.

In its present arrangement, magnetic field lines create closed loops: above Earth’s surface, they run from south to north, before returning from north to south far beneath it.

However, the field’s polarity occasionally reverses at random. If such a switch happened now, compasses that point north would instead indicate the South Pole.

The Laschamps event 41,000 years ago

The most recent reversal of this kind took place roughly 41,000 years ago and left its mark in the Laschamps lava flows of France. As the field fell to just 5 percent of its present intensity, the reversal enabled an excess of cosmic rays to enter Earth’s atmosphere.

Ice cores and marine sediments retain isotopic evidence of this unusually intense solar bombardment. A study published last year found that beryllium-10 isotope levels doubled during the Laschamps event.

These modified atoms arise when cosmic rays interact with the atmosphere, ionising the air and frying the ozone layer. Since global climate change may result, researchers have speculated that the event could be linked to the extinction of Australia’s megafauna and to changes in how humans used caves.

“Understanding these extreme events is important for their occurrence in the future, space climate predictions, and assessing the effects on the environment and on the Earth system,” German Research Center for Geosciences geophysics Sanja Panovska explained at the time.

The Laschamps reversal unfolded over 250 years, then remained in its unusual alignment for approximately 440 years. During this period, Earth’s magnetic field may at its strongest have been only 25 percent as powerful as it is today, while the north polarity shifted southwards.

Swarm satellites monitor magnetic anomalies

More recent magnetic anomalies, including weakening over the Atlantic Ocean, have prompted questions over whether another reversal may be approaching. Yet recent research indicates that these irregularities are not necessarily associated with polarity-flipping events.

The South Atlantic anomaly does, nevertheless, expose satellites passing through the region to greater radiation levels.

Since 2013, ESA’s Swarm constellation has monitored magnetic signals originating in Earth’s core, mantle, crust, oceans, ionosphere and magnetosphere. These measurements help scientists understand the planet’s geomagnetic field more clearly and forecast its variations.

An earlier version of this article was published in October 2024.