MAGNETIC FLIP-FLOP

Earth's magnetic field, our shield against cosmic radiations, has a history of reversals and anomalies. From setting up observatories and satellites to analysing ship logs and archeological surveys, scientists are piecing together its past to uncover clues about future shifts. Yet, many mysteries remain

- ROHINI KRISHNAMURTHY

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.