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Earth’s magnetic field serves as a protective barrier against cosmic radiation from space. But this shield isn’t always as stable as it appears.
There are some short-lived episodes when the magnetic north wanders, occasionally switching with the south pole. This natural process, known as magnetic field excursions, reduces the strength of the magnetic field.
One well-known example of a magnetic field excursion is the Laschamps event, which happened around 41,000 years ago. Along with the upside-down compass, this occurrence dramatically weakened the strength of Earth’s magnetic field.
The reduced intensity meant the magnetic fields could not deflect charged particles away from the planet, as they typically do. The event exposed Earth’s atmosphere and surface to dangerous cosmic rays as well as a steady bombardment of charged particles from the Sun.
“Periods of low magnetic field intensity could correlate to major upheavals in the biosphere,” mentioned the press release.
Understanding the event
When cosmic rays penetrate Earth’s atmosphere, they interact with the nuclei of atmospheric atoms. This interaction results in the formation of cosmogenic radionuclides. These isotopes are referred to as cosmogenic since they come from cosmic rays.
To understand these events, scientists at the GFZ Potsdam in Germany examined cosmogenic radionuclides trapped in ice and marine sediment cores.
The analysis of these isotopes may reveal information about the period when Earth’s surface was intensively bombarded with cosmic rays.
In this new study, researchers attempted to unravel the link between paleomagnetic field strength and cosmogenic nuclides during the Laschamps excursion. Paleomagnetic field intensity is the strength of the Earth’s magnetic field in the past or during this excursion.
Moreover, these isotopes may be created by cosmic rays interacting with atoms in Earth’s atmosphere, such as beryllium-10.
The team suggests that during a weak paleomagnetic field, the production rate of cosmogenic radionuclides would have drastically increased in Earth’s atmosphere. The researchers looked into the fluctuation of beryllium-10, which acts as a marker for changes in magnetic field intensity in the distant past.
The study’s importance for space climate predictions
The researchers mentioned in the press release that they found that “the average production rate of beryllium-10 during the Laschamps excursion was two times higher than present-day production, implying very low magnetic field intensity and lots of cosmic rays reaching Earth’s atmosphere.”
Earth’s protective magnetosphere shrunk as the magnetic field decreased, potentially exposing our ancestors to extreme cosmic radiation some 41,000 years ago.
“Understanding these extreme events is important for their occurrence in the future, space climate predictions, and assessing the effects on the environment and on the Earth system,” said Sanja Panovska, a researcher at GFZ Potsdam in the press release.
Panovska will be presenting this new study at the European Geosciences Union (EGU) General Assembly 2024 in Vienna, Austria
