The Earth's geomagnetic field undergoes periodic changes, such as the oscillation of magnetic north and occasional reversals where north and south swap places. When these phenomena occur, the strength of the planet's geomagnetic field temporarily decreases.
This is precisely what happened between 42,200 and 41,500 years ago. Instead of a permanent reversal, there was a sudden change in the strength of the magnetic field, accompanied by a variation in the orientation of the poles by around 45 degrees.
Known as the Laschamps event, it represented what scientists call a geomagnetic excursion and, as well as being the first known event of its kind, it also continues to be the most studied.
During geomagnetic excursions, the low intensity of the magnetic field causes a reduction in protection against cosmic radiation, an event that could cause significant impacts on Earth.
By measuring the radionuclides found in cores extracted from marine sediments and ice that has accumulated over very long periods, scientists are able to determine the periods when the greatest quantities of cosmic rays bombarded the planet.
The isotopes that result from the interactions between the Earth's atmosphere and cosmogenic radiation can be used as indicators of periods when cosmic rays actually managed to hit our planet.
According to researcher Sanja Panovska, quoted by EurekAlert, the intensity of the magnetic field was significantly impacted during the Laschamps event, a suggestion confirmed by the cosmogenic nuclides detectable in core samples.
The research suggested that a specific radionuclide, beryllium-10, is a good mirror of the changes that took place during the Laschamps excursion, with an average production rate of the radioactive isotope shown to be twice as high around 41,000 years ago.
The scientist from GFZ Potsdam in Germany will present the results of her study at the European Geosciences Union (EGU) General Assembly next week. At the event, the researcher will also reveal new information from paleomagnetic data and data related to radionuclides of cosmic origin, which provided the team with the material needed to produce reconstructions.
According to the models, the Earth's magnetosphere retreated as the geomagnetic field decreased, reducing protection against cosmic rays over a period of time.
