The Earth is surrounded by a magnetic cocoon that protects it from the onslaught of cosmic rays streaming through space, and (as we often hear) from the impact of charged particles ejected by the Sun. We have also heard many times that the geomagnetic field is not constant. Not only can it “wander”, with the result that magnetic north does not match geographic north (and changes over time), but it can also completely reverse itself and then north becomes south and south becomes north – yes, that's famous polarity.
But there is another phenomenon that you may not have heard about. this Magnetic field incidentsThese are short periods during which the magnetic field strength decreases and the familiar two magnetic poles can disappear or be replaced by multiple magnetic poles. It is one of the best studied phenomena of this type Lachamp happenedWhich occurred on 41,000 years ago. A lower magnetic field strength means less protection of the Earth's surface from harmful cosmic radiation.
The Earth is like a big book in which various events of its history are recorded. You just need to learn to read it. To see the radiation bombarding Earth, scientists can measure, for example, cosmic radionuclides in ice cores or marine sediments. These isotopes are created by the interaction of cosmic rays with the Earth's atmosphere.
Search the old Geomagnetic excursionsthat is, short-term changes in field strength with a change in the direction of the poles up to 45 degrees from the previous position, and it can be noted that periods of low ancient magnetic field strength (“paleo”, i.e. in the Earth’s past) should be associated with a higher rate of production of cosmic radionuclides in Atmosphere.
Sanja Banovska from the German Research Center for Geosciences GFZ (GeoForschungsZentrum) has studied radionuclides such as beryllium-10, which are a very good indicator of changes in the Earth's ancient magnetic density. It found that the average rate of beryllium-10 production during the Lachamp event was twice what it is today, which means a very low magnetic field strength and therefore a large amount of radiation reaching the atmosphere.
Source literature: Banovska, S.: Long-term changes in the geomagnetic field: progress, challenges and recent applications, European Union General Assembly 2024, Vienna, Austria, 14-19 April 2024, EGU24-10977, https://doi.org/10.5194/egusphere- egu24-10977, 2024
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