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Earth’s Magnetic Field
Magnetic flip-flop
Context:
In 2022, Scientists unveiled a soundtrack at Solbjerg Square, Copenhagen, converting Earth’s magnetic signals from 32 locations into sound to showcase the planet’s magnetic field and its fluctuations over the past 100,000 years.
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- In 2024, a new soundtrack recreated the Laschamps geomagnetic excursion (41,000 years ago), when Earth’s magnetic field weakened to 5% of its current strength and poles temporarily switched.
- Laschamps involved a temporary reversal of magnetic poles and had an eerie, alien-like sound.
- Both soundtracks are based on research by Sanja Panovska (GFZ German Research Centre, Potsdam).
- A new composition on the Brunhes-Matuyama reversal (780,000 years ago) is expected later in 2025 and is predicted to sound different from Laschamps.
Historical Data
- In the past 83 million years, Earth’s magnetic poles have reversed 183 times.
- Excursions occur 10 times more often than reversals.
- Since the Brunhes-Matuyama reversal, three major excursions occurred:
- Norwegian-Greenland Sea event (~64,500 years ago)
- Laschamps (~41,000 years ago)
- Mono Lake (~34,500 years ago)
- Prediction is difficult due to no clear periodicity.
Nature and Origin of Earth’s Magnetic Field
- Earth behaves like a giant magnet with field lines from the magnetic north to south.
- The magnetic field originates 2,900 km beneath the surface in the liquid outer core, powered by electric currents from molten iron movement.
- It creates a protective bubble extending into space, deflecting harmful solar and cosmic radiation.
Reversals vs Excursions
- Reversals: Occur when the magnetic polarity change lasts more than 100,000 years.
- Excursions: Temporary shifts in polarity lasting less time.
- Magnetic field fluctuations are driven by fluid motion in the outer core, itself powered by heat from the inner core and Earth’s rotation.
- Clockwise fluid flow = normal polarity; anticlockwise = reversal.
Field Strength and Future Predictions
- The magnetic field has weakened by 10% over the past 200 years.
- At the current rate, it could decline to zero in 1,500–1,600 years, prompting questions about a potential reversal or excursion.
Impact on Climate and Life
- A 2021 Science study linked Laschamps to ozone changes and climate shifts at mid-to-high latitudes.
- It also observed overlapping extinction phases, hinting at possible links.
- However, Panovska’s unpublished study found no impact of Laschamps on Neanderthal extinction, citing protection by Earth’s atmosphere.
- A 2019 Science Advances study estimated the Brunhes-Matuyama reversal took 22,000 years, allowing generational adaptation to future instability.
Drifting Magnetic Poles
- The north magnetic pole has moved 1,100+ km from the Canadian Arctic to Siberia since 1831.
- Speed increased from 16 km/year in the 1990s to 35 km/year today.
- The south magnetic pole is more stable, moving just 5 km/year.
- Disparity is likely due to turbulence in the outer core, though not fully understood.
Advances and Tools in Magnetic Research
- Use of geomagnetic observatories (past 100 years) and satellite data (past few decades).
- Historical data from ship logs since 1590 help trace changes in compass directions.
- Geological samples provide deeper time insights:
- Lava rocks, lake/ocean sediments, and ancient pottery retain magnetic signatures.
- Stronger magnetic fields align more grains in sediments, resulting in stronger magnetisation.
- In Uttarakhand, India, researchers found evidence of two excursions:
- Bagwalipokar I (15,500–14,700 years ago)
- Bagwalipokar II (8,000–2,850 years ago)
Cosmogenic Isotopes and Excursions
- 2023 JGR Space Physics study by Panovska used beryllium-10 and carbon-14 in ice cores and sediments.
- During Laschamps, beryllium-10 production doubled due to weaker shielding from cosmic rays.
- Isotopes form via cosmic rays interacting with oxygen and nitrogen, then fall with precipitation.
South Atlantic Anomaly (SAA)
- A region over South America and South Africa where the magnetic field is weakest.
- Allows harmful cosmic radiation to reach spacecraft in low Earth orbit.
- A 2018 PNAS study found no evidence linking SAA to magnetic reversals.
- SAA-like features occurred 6–9 times in the past 100,000 years, with the field recovering each time.
- Suggests a reversal is not imminent.
Forecasting the Magnetic Field
- Scientists can predict magnetic behaviour up to five years into the future.
- World Magnetic Model (WMM) updated in December 2024 by the US NGA and UK Defence Geographic Centre.
- Forecasts are made by extrapolating recent trends.
- Future advances in computational modelling are expected to improve resolution and forecasting accuracy.
