Cosmic rays penetrated the Earth's 'shield' 41,000 years ago

April 19 () –

Earth's magnetic field protects us from dangerous radiation from space, but 41,000 years ago cosmic rays They passed through the atmosphere of our planet.

Scientists present new information about that “excursion” phenomenon in which our planet's magnetic field decreased and harmful space rays bombarded the planet.

Earth's magnetic field protects our planet from the attack of cosmic radiation flowing through space and at the same time protects us from charged particles thrown out by the sun. But the geomagnetic field is not stationary. Magnetic north not only wobbles away from true north (a geographically defined location), but occasionally reverses. During these reversals, north becomes south, south becomes north, and in the process, The intensity of the magnetic field decreases.

But there are also something called magnetic field excursions, brief periods in which the intensity of the magnetic field decreases and the dipole (or two magnetic poles) that we know can disappear, replaced by multiple magnetic poles.

The Laschamps excursion, which took place about 41,000 years ago, is among the best studied. It has a low magnetic field intensity that implies less protection for the Earth's surface from harmful space rays. Periods of low magnetic field intensity could correlate with major disruptions in the biosphere.

To see when cosmic rays were intensely bombarding the Earth's surface, Scientists can measure cosmogenic radionuclides in cores of both ice and marine sediments. These special isotopes are produced by the interaction between cosmic rays and the Earth's atmosphere; They are born from cosmic rays, that is why they are cosmogenic.

Moments of lower paleomagnetic field intensity (less shielding) should correlate with higher rates of cosmogenic radionuclide production in the atmosphere. Sanja Panovska, researcher at GFZ Potsdam, Germany, presents her findings on the relationship between paleomagnetic field strength and cosmogenic nuclides during the Laschamps excursion, focusing on space weather, during the 2024 General Assembly of the European Geosciences Union (EGU).

Variations in cosmogenic radionuclides such as beryllium-10 provide an independent indicator of how Earth's paleomagnetic intensity changed. In fact, Panovska discovered that the average production rate of beryllium-10 during the Laschamps excursion was twice the current productionwhich implies a very low magnetic field intensity and many cosmic rays that reach the Earth's atmosphere.

To gain more insight from the paleomagnetic and cosmogenic radionuclide data, Panovska reconstructed the geomagnetic field using both data sets. Her reconstructions show that during Laschamps' excursion, the magnetosphere contracted as the field decreased dramatically, “thus reducing the shielding of our planet”said.

“Understanding these extreme events is important for their future occurrence, space weather predictions, and assessment of effects on the environment and the Earth system.”