The Earth’s atmosphere was penetrated by powerful cosmic rays 41 thousand years ago

Scientists have made a new report on the event known as the “Kargapolovo-Laschamp geomagnetic excursion”, which occurred 41 thousand years ago. Then the magnetic field of our planet began to turn and weakened greatly, and powerful cosmic rays penetrated its atmosphere.

The Earth. Source:

Why do cosmic rays not reach the Earth’s surface

The Earth’s magnetic field protects us from dangerous cosmic radiation, but it is not as constant as we used to think. At the General Assembly of the European Geosciences Union, a group of researchers presented new information about the event known as the “Kargapolovo-Laschamp excursion”. It lies in the fact that 41 thousand years ago the magnetic field of our planet weakened, and harmful cosmic rays bombarded the planet.

Usually, the Earth’s magnetic field covers our planet with a cocoon from the onslaught of cosmic radiation that permeates the entire cosmos, including from charged particles that are thrown out by the Sun. But it is not stationary. The magnetic north not only fluctuates, deviating from the true north (geographically defined location), but also turns over from time to time. During these events, the magnetic north becomes the south and vice versa, and the intensity of the field itself decreases.

Magnetic field excursion

But there are also so-called magnetic field excursions — short periods when the intensity of the magnetic field decreases, and the familiar dipole may disappear, replaced by several magnetic poles. 

The Kargapolovo-Laschamp excursion, which occurred about 41,000 years ago, is one of the most studied. It is characterized by a low magnetic field strength, which means less protection of the Earth’s surface from harmful cosmic radiation. Periods of low magnetic field intensity may correlate to major upheavals in the biosphere.

To see when cosmic rays intensely bombarded the Earth’s surface, scientists can measure cosmogenic radionuclides in ice cores and marine sediments. These special isotopes are formed when cosmic rays interact with the Earth’s atmosphere.

Connection of cosmic radionuclides and the Earth’s magnetic field

Obviously, periods of lower intensity of the paleomagnetic field, when it cannot shield the Earth, should correlate with higher rates of formation of cosmogenic radionuclides in the atmosphere. Sanja Panovska, a researcher from Germany, presented her findings on the relationship between the intensity of the paleomagnetic field and cosmogenic nuclides during the Laschamps space climate excursion next week during the General Assembly of the European Geosciences Union (EGU) 2024.

Variations of cosmogenic radionuclides, such as beryllium-10, are an independent indicator of how the Earth’s magnetic field has changed in the past. Panovska found that the average level of beryllium-10 production during the Kargapolovo-Laschamp excursion was twice as high as today. This means a very low magnetic field strength and a large number of cosmic rays reaching the Earth’s atmosphere.

To get more information from cosmogenic radionuclide and paleomagnetic data, Panovska reconstructed the situation using both datasets. Her research showed that 41 thousand years ago, the magnetosphere was greatly compressed and practically did not protect the Earth from radiation.

According to

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