The Earth is constantly bombarded by high-energy charged particles called cosmic rays. We are normally protected from this barrier by the Earth’s magnetic bubble, the magnetosphere. So what happens when this shield weakens?

Cosmic rays are basically hydrogen nuclei thrown into space by powerful celestial events such as supernovae and the death of massive stars. These incredibly energetic particles are often captured by the magnetosphere, which also protects us from harsh solar radiation from the sun.

However, the magnetosphere is not a monolithic, immutable entity. Not only does magnetic north “oscillate” slightly from geographic “true north,” but the entire magnetosphere “rotates” from time to time. This causes the north pole of the area to transform into the south pole and the density of the area to decrease.

In addition, there are other short periods when the two magnetic poles of the magnetosphere are replaced by more than one magnetic pole. During these periods, called “magnetic field excursions”, the strength of the magnetic poles also weakens, which means that our planet is less protected from cosmic radiation during this period.

The question is: Are periods of low magnetospheric density also associated with major upheavals in Earth’s biosphere, that is, the entire region of our planet where life exists, from mountain peaks to the deepest ocean trenches?

“Understanding these extreme events is important to assess their future occurrence, predict the space climate, and assess the impact on the environment and the Earth system,” said Sania Panovska, a scientist at GFZ Potsdam in Germany.

Scientists can measure the content of different isotopes to identify periods when the Earth was subjected to more cosmic ray bombardment than usual. These are variants of an element with different numbers of neutrons in the atomic nucleus.

When cosmic rays hit particles in Earth’s atmosphere, they create showers of isotopes called “cosmogenic radionuclides” that rain down on our planet’s surface. Along with ice cores excavated from regions such as Antarctica and Greenland, they accumulate over time in sediments that scientists can study after they are pulled from the seafloor.

A well-studied example of a magnetic field excursion is the Laschamps excursion, which occurred approximately 41,000 years ago. Panovska studied the relationship between the density of the Earth’s magnetosphere during this event and the concentration of cosmogenic radionuclides such as beryllium-10.

He found that the average production rate of beryllium-10 has doubled compared to the rate at which this cosmogenic radionuclide is produced today under cosmic ray bombardment. This indicates a very low magnetospheric intensity during the trip to Laschamps; This results in significantly more cosmic rays reaching the Earth’s atmosphere and creating showers of secondary particles.

Panowska used these measurements to reconstruct Earth’s magnetosphere and found that it contracted as its strength decreased during this event. He hopes this reconstruction will help him and his fellow scientists learn more about cosmogenic radionuclides and bombardment with cosmic rays.