Trunks of pine trees buried in a bank of the Durance River in the southern French Alps show evidence of a powerful solar storm that happened 14,300 years ago. Such storms are produced when very large flares erupt out of the sun.
Recently, Tim Heaton at the University of Leeds in the United Kingdom and his colleagues found evidence of the solar storm in those tree trunks after the river bank eroded and exposed them. A significant rise in the levels of radioactive carbon-14 alerted Heaton and his colleagues to the powerful event.
They compared the tree rings, and they constructed a timeline of when each tree lived to calculate when the event happened, according to an article in New Scientist magazine, a free sample issue distributed in early March 2024. The article, titled Largest Known Solar Storm Struck Earth 14,300 Years Ago, was written by Alex Wilkins.
Heaton and his team found evidence that showed another area of the world was also affected by the event. Some Greenland ice cores have elevated levels of beryllium. Those levels can be produced in a way similar to carbon-14.
Other evidence of similar solar flares have also been discovered. Fusa Miyake discovered evidence of a powerful solar flare that affected tree trunks at Nagoya University in Japan. The 2012 discovery shows how the solar storm, made up of charged particles from the sun as well as magnetized plasma and gamma rays, caused a spike in the trees' carbon-14 levels.
France, Japan and Greenland are not the only places where evidence exists of massive solar storms. At least nine such possible solar storms, called Miyake events, have been found.
No one knows what such a powerful solar storm would do to our world today. The largest solar storm experienced in recent history occurred in 1859. Called the Carrington event, it was named after one of the two British astronomers who observed it. The solar storm caused fires and produced currents in telegraph wires.
Though it had an impact on Earth, the storm was so tiny it would not have registered in the radiocarbon record. A storm as huge as the one that happened 14,300 years ago might be catastrophic or it might be much less destructive, depending on who you ask.
Scientists don't know for sure what caused the powerful solar storm. It might have been at the extreme end of moderate solar storms that occur frequently, or it could have been an unusual, special behavior of the sun.
Whatever the cause, trees recorded the event in their trunks, and researchers have begun to discover the evidence.