Is there something strange and alien confined deep inside the Earth? Is it trying to break free and escape into the heavens? No, of course not.
But in a new soundscape from the ESA, it sure sounds like it.
About every 450,000 years, Earth’s magnetic poles flip. North becomes south and vice versa in a phenomenon called geomagnetic reversal. This discovery was shocking since the planet’s magnetic field is such a foundational part of our environment. However, these reversals appear to be mostly harmless to life.
Geomagnetic reversals are chaotic events. Though they occur on average about every 450,000 years, there’s no pattern to them. There have been about 183 of them in the last 83 million years, leading us to the 450,000-year number. But the last one was 780,000 years ago, and some say that we’re overdue for the next one.
Sometimes, the events are excursions rather than full reversals. That’s when the field shifts for several hundred years and then returns to its original orientation, like the Laschamps event about 41,000 years ago. In an excursion, the field reverses in Earth’s outer core while its inner core remains unchanged. These happen more frequently than full reversals, but their exact number and timing are more difficult to determine since their effects aren’t global.
The evidence for these reversals and excursions is found in paleomagnetism. Paleomagnetism measures the orientation of magnetic elements like iron in volcanic rock as it cools. By determining the age of the rock, scientists can determine the orientation of Earth’s magnetic field when the rock solidified. The history of Earth’s magnetic reversals is recorded where new magma cools as the seafloor spreads.
During these excursions and reversals, the magnetic field’s strength weakens. During the Laschamps event, which lasted several hundred years, the field weakened to only 5% of its normal strength.
Earth’s magnetic fields deflect cosmic rays away from Earth, and at only 5% of its normal strength, the field lets in far more cosmic rays than usual. Cosmic rays are high-energy particles, usually protons or atomic nuclei, that come from the Sun and from objects both inside and outside of the Milky Way and travel at relativistic speeds. When they strike Earth’s atmosphere, they produce showers of secondary particles.
No matter how often they occur or what causes them, scientists are pretty sure that the Laschamps event was the latest excursion, and the European Space Agency decided it would be good if we knew what it sounded like.
The ESA launched its three-satellite Swarm mission in 2013 to study Earth’s magnetic fields. Swarm measures magnetic signals not only from the core but also from the mantle, the oceans, and all the way up to the ionosphere and magnetosphere. Scientists at the Technical University of Denmark and the German Research Centre for Geosciences used Swarm data and data from other sources to create a soundscape of the Laschamps event.
The scientists used recordings of natural sounds, such as rocks falling and wood creaking, and blended them into alien-like sounds that were both familiar and strange. The result sounds Earthly, subterranean, natural, and creepy all at the same time as if some ancient part of the Earth is writhing around inside the planet, which, in a way, it is.
The first version was created in 2022 and was played as a sort of public art installation in Copenhagen. There were 32 speakers, and each one played the sound represented by changes in the magnetic field at 32 locations around the world.
Check out the ESA’s SoundCloud channel, where they post their audio creations.