Earth's magnetic field intermittently shielded us during cosmic ray influx 41,000 years ago

Earth's magnetic field intermittently shielded us during cosmic ray influx 41,000 years ago
by Robert Schreiber
Berlin, Germany (SPX) Apr 22, 2024

Earth's geomagnetic field, while generally shielding the planet from cosmic and solar radiation, experiences periods of significant fluctuation. Not only does the magnetic north shift from its geographically defined true north, but it also undergoes complete reversals. During such reversals, previously defined poles swap positions, causing a noticeable decrease in the magnetic field's strength.

These fluctuations also include magnetic field excursions, temporary states where the dipole reduces in intensity and multipolar configurations emerge. A prominent example is the Laschamps excursion around 41,000 years ago, characterized by a significantly weaker magnetic field, which resulted in reduced protection against harmful cosmic radiation. This period coincides with notable disruptions in Earth's biosphere.

To analyze periods of intense cosmic radiation, researchers study cosmogenic radionuclides found in ice and marine sediment cores. These isotopes, formed from cosmic rays interacting with the atmosphere, serve as markers for the times when Earth's magnetic shield was diminished.

A key focus is on periods when lower geomagnetic field intensity correlates with increased production of cosmogenic radionuclides, such as beryllium-10. Researcher Sanja Panovska from GFZ Potsdam, Germany, discusses the interplay between paleomagnetic field intensity and these nuclides during the Laschamps excursion at the upcoming European Geosciences Union General Assembly 2024.

Her findings indicate a doubled production rate of beryllium-10 compared to present-day levels, signifying a substantial decrease in geomagnetic protection and consequently, higher cosmic ray penetration during the Laschamps excursion. Panovska further utilized both cosmogenic radionuclide and paleomagnetic data to reconstruct historical geomagnetic fields, revealing significant reductions in the Earth's magnetic shielding.

This research not only charts historical geomagnetic fluctuations but also enhances understanding of potential future extreme events, aiding predictions of space climate impacts and their environmental consequences.

Research Report:Long-term changes of the geomagnetic field: recent progress, challenges and applications