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When Earth’s Magnetic Shield Weakened: Cosmic Ray Invasion 41,000 Years Ago

Studies show a big rise in cosmogenic radionuclides during the Laschamps excursion, suggesting decreased geomagnetic shielding and possible biosphere disturbances. Earth’s magnetic field cocoons…

Cosmic Rays Earth Atmosphere Art

A new study investigates how the decrease in geomagnetic field strength is connected to an increase in cosmogenic radionuclides like beryllium-10 during the Laschamps excursion, highlighting its impact on Earth’s defense against space radiation. Credit:

Studies suggest a notable rise in cosmogenic radionuclides during the Laschamps excursion, indicating decreased geomagnetic protection and potential disruptions to the biosphere.

Earth’s magnetic field envelops our planet from the influx of cosmic radiation traveling through space while also guarding us from charged particles propelled outward by the sun. However, the geomagnetic field is not fixed. Not only does magnetic north fluctuate, deviating from true north (a geographically defined location), but occasionally, it flips. During these reversals, north becomes south, south becomes north, and the strength of the magnetic field diminishes.

Magnetic Field Excursions

But there are also events called magnetic field excursions, brief periods in which the strength of the magnetic field diminishes and the dipole (or two magnetic poles) that we’re familiar with can vanish, replaced by multiple magnetic poles. The well-studied Laschamps excursion that took place approximately 41,000 years ago is one example. It exhibits a low magnetic field strength signifying reduced protection for Earth’s surface from harmful space rays. Instances of low magnetic field intensity may correspond to significant disturbances in the biosphere.

Measuring Impact of Cosmic Rays

To determine when cosmic rays were intensely bombarding Earth’s surface, scientists can analyze cosmogenic radionuclides in cores from both ice and marine sediment. These unique isotopes are created by the interaction between cosmic rays and Earth’s atmosphere; they originate from cosmic rays, hence they are cosmogenic.

Research Discoveries on Space Climate

Periods of lower paleomagnetic field intensity—less protection—should align with higher rates of cosmogenic radionuclide production in the atmosphere. Sanja Panovska, a researcher at GFZ Potsdam, Germany, will present her findings about the connection between paleomagnetic field intensity and cosmogenic nuclides during the Laschamps excursion, focusing on the space climate, next week during the European Geosciences Union (EGU) General Assembly 2024.

Fluctuations in cosmogenic radionuclides such as beryllium-10 offer an independent measure of how Earth’s paleomagnetic intensity changed. Indeed, Panovska discovered that the average generation rate of beryllium-10 during the Laschamps excursion was double the present-day production, indicating very low magnetic field strength and an abundance of cosmic rays reaching Earth’s atmosphere.

Geomagnetic Reconstructions

To extract more information from both cosmogenic radionuclide and paleomagnetic data, Panovska reconstructed the geomagnetic field using both sets of data. Her reconstructions demonstrate that during the Laschamps excursion, the magnetosphere decreased when the field significantly diminished, “thus diminishing the protection of our planet,” she said. “Understanding these extreme events is crucial for predicting their occurrence in the future, space climate forecasting, and evaluating the impacts on the environment and the Earth system.”

To find out more about this research, Panovska will present it verbally at EGU 2024 on Friday, 19 April, 14:05-14:15 CEST, Room -2.20 during session EMRP3.3

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