When Earth’s magnetic shield faltered: a glimpse into cosmic ray bombardment 41,000 years ago

Credit: NASA.

Earth is constantly shielded from harmful cosmic radiation and solar particles by its magnetic field.

However, scientists have discovered that this protection isn’t always as robust as we might think.

At the European Geosciences Union General Assembly, researchers presented new findings about a time, 41,000 years ago, when Earth’s magnetic shield weakened significantly.

Our planet’s magnetic field acts like a protective cocoon, diverting cosmic radiation and solar particles away from us.

This field isn’t fixed; it shifts, and occasionally, the magnetic poles even flip — north becomes south and vice versa. During these flips, the strength of the magnetic field decreases.

There are also shorter episodes, known as magnetic field excursions, where the magnetic field’s intensity drops temporarily.

One well-studied event is the Laschamps excursion around 41,000 years ago. During this time, the magnetic field was much weaker, providing less protection from space radiation.

The reduction in the magnetic field’s strength during these periods means more cosmic rays can penetrate our atmosphere.

Scientists study this by looking at cosmogenic radionuclides found in ice cores and marine sediments. These are special isotopes created when cosmic rays interact with our atmosphere.

Sanja Panovska, a researcher from GFZ Potsdam, Germany, shared her study findings at the EGU General Assembly 2024.

She investigated the relationship between the intensity of the paleomagnetic field and the production of cosmogenic radionuclides during the Laschamps excursion.

Her research showed that during this time, the production rate of a radionuclide called beryllium-10 was double what it is today, suggesting a significantly weaker magnetic field. This means a lot more cosmic rays were reaching the Earth.

By combining data on cosmogenic radionuclides with paleomagnetic data, Panovska was able to reconstruct changes in the geomagnetic field.

Her reconstructions show that during the Laschamps excursion, Earth’s magnetosphere, the area affected by our magnetic field, shrank considerably. This reduced the protective barrier against cosmic radiation.

Understanding these periods of weakened magnetic protection is crucial for predicting future changes in the magnetic field, the space climate, and their potential effects on Earth and its environment.

This research not only offers insights into past events but also helps us prepare for possible future scenarios where Earth’s magnetic shield might falter again.