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  Reeth Informal

 Astronomy Group

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Gigantic Solar Flares: their impact on Earth - Les Knight – April 2020

At the February 2020 meeting of the group Mike Evershed reported back on a number of recent astronomy talks he had attended. One of these was about giant coronal outbursts from the Sun and their possible impact on the Earth. This intrigued me and so I set out to find what, if any, historical evidence there was for their impact.

The Earth is constantly bombarded by high energy particles from deep space and the Sun. The most obvious manifestation of these are the aurorae. However, high energy particles are known to interact with both the atmosphere and exposed rocks in a number of ways which have provided useful dating methods. The most widely is known is the interaction with atmospheric nitrogen to produce carbon-14 (C-14) which is radioactive. All living organisms incorporate some C-14 during their lifetime which on their death starts to decrease by radioactive decay. The amount of C-14 can therefore be used to measure how long it is since the organism died and is the basis of C-14 dating much used in archaeology. However, high energy particles can also interact with rocks exposed at the Earth’s surface generating exotic aluminium, beryllium and chlorine isotopes. The concentration of these isotopes can be used to determine how long a rock has been exposed at the Earth’s surface to date events such as landslides etc.   

All these dating methods assume that the rate of high energy particle bombardment and hence production of the new isotopes, has remained constant over time. However, it soon became apparent that the ages produced by C-14 dating did not match exactly historic dates (Egyptian dynasties) and dates obtained from counting tree rings (dendrochronology). Detailed analysis of individual annual tree rings and subsequently annual snow layers in ice cores from Greenland and Antarctica showed that the flux of particles has not been constant.  Today C-14 dates are ‘calibrated’ to take account of these changes.