The Earth is constantly bombarded by high-energy charged particles called cosmic rays. We are normally shielded from such attacks by Earth’s magnetic bubble, or magnetosphere. But what happens when this shield weakens?
Cosmic rays are primarily hydrogen nuclei ejected into space by powerful celestial events, such as the supernova deaths of massive stars. These incredibly high-energy particles are normally intercepted by the magnetosphere, which also protects us from intense solar radiation from the sun.
However, the magnetosphere is not a monolithic, unchanging entity. Not only does magnetic north “wiggle” slightly away from geographical “true north,” but the entire magnetosphere occasionally “flips.” This causes the north pole of the magnetic field to become south and vice versa, with the magnetic field’s strength weakening in the process.
Beyond this, there are other brief periods when the two poles of the magnetosphere “disappear” and are replaced by multiple poles. During these periods, known as “magnetic excursions,” the strength of the magnetic poles also weakens, meaning our planet is less protected from cosmic rays during these periods.
related: Where do cosmic rays come from?
The question is, are periods of low magnetospheric strength also associated with major upheavals in Earth’s biosphere?
Sanja Panovska, a scientist at GFZ Potsdam, Germany, said in a statement: “Understanding these extreme events is important for their future occurrence, space climate prediction, and for assessing their impact on the environment and Earth systems. “
To determine when Earth experienced a heavier than usual bombardment from cosmic rays, scientists can measure the abundance of different isotopes. These are variations of elements that have different numbers of neutrons in their nuclei.
When cosmic rays hit particles in Earth’s atmosphere, they create showers of isotopes called “cosmic radionuclides” that fall onto our planet’s surface. Over time, these materials accumulate in sediments, and scientists can study them after recovering them from the seabed and in ice cores drilled from areas such as Antarctica and Greenland.
A well-studied example of a magnetic field shift is the Lachand shift, which occurred about 41,000 years ago. Panowska has been studying the relationship between the strength of Earth’s magnetosphere and the concentration of cosmic radioactive species such as beryllium-10 during this event.
She found that the average production rate of beryllium-10 doubled compared to the rate at which this cosmic radionuclide is produced by today’s cosmic ray bombardments. This suggests that the magnetospheric strength was very low during the Laschan excursion, causing more cosmic rays to reach the Earth’s atmosphere and create 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. She hopes the reconstruction will help her and other scientists learn more about cosmic radionuclides and cosmic ray bombardments.
Panowska presented the cosmic ray discovery at the 2024 European Geosciences Union (EGU) Congress on Friday (April 19).
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Image Source : www.space.com