Earth got hammered by cosmic rays 41,000 years ago due to a weak magnetic field
"Understanding these extreme events is important for their occurrence in the future, space climate predictions and assessing the effects on the environment and on the Earth system."
Earth is under constant bombardment by high-energy charged particles called cosmic rays. We're normally shielded from this barrage by Earth's magnetic bubble, the magnetosphere. But what happens when this shield weakens?
Cosmic rays are primarily hydrogen nuclei blasted into space by powerful celestial events such as the supernova deaths of massive stars. These incredibly energetic particles are normally intercepted by the magnetosphere, which also protects us from harsh solar radiation from the sun.
The magnetosphere is not a monolithic, unchanging entity, however. Not only does magnetic north "wobble" slightly away from geographic "true north," but the entire magnetosphere occasionally "flips." This results in the field's north pole becoming south and vice versa, with the intensity of the field waning in the process.
In addition to this, there are other brief periods during which the two magnetic poles of the magnetosphere "disappear," to be replaced by a multitude of magnetic poles. During these periods, called "magnetic field excursions," the strength of magnetic poles also weakens, implying that our planet is less well-protected from cosmic rays at these times.
