The Sun is going through a period of high activity, but it is nothing compared to an enormous solar event that slammed into our planet 14,000 years ago. If one were to occur today, the effect on Earth could be devastating.
The oldest trees on Earth date back a whopping 5,000 years, living through all manner of events. They have stood through the rise and fall of the Roman Empire, the birth of Christianity, the European discovery of the Americas and the first Moon landing. Trees can even be fossilised in soil underground, giving us a connection to the last 30,000 years.
At first glance, these long-lived specimens might just appear to be static observers, but not so. They are doing something extraordinary as they grow – recording the activity of our Sun.
As trees photosynthesise throughout the year, they change in colouration depending on the season, appearing lighter in spring and darker by autumn. The result is a year-on-year record contained within the growth “rings” of the tree. “This gives us this really valuable archive of time capsules,” says Charlotte Pearson, a dendrochronologist – someone who studies tree rings – at the Laboratory of Tree-Ring Research at the University of Arizona, US.
For most of the 20th Century, dendrochronologists have largely used tree rings to investigate change across wide chunks of history – a decade or more. Yet at certain points in time, the change they document has been more sudden and cataclysmic. What they are finding evidence of are massive solar events that reveal disturbing insights into the turbulent recent past of the star at the centre of our Solar System.
“Nobody was expecting a brief event to appear,” says Edouard Bard, a climatologist at the College de France in Paris. But in 2012 a then-PhD student called Fusa Miyake, now a cosmic ray physicist at Nagoya University in Japan, made an astonishing discovery. Studying Japanese cedar trees, she discovered a huge spike in a type of carbon known as carbon-14 in a single year nearly 800 years ago, in 774 CE. “I was so excited,” says Miyake.
After doubting the data at first, Miyake and her colleagues soon came to an unnerving conclusion. The spike in carbon-14 must have come from something injecting huge numbers of particles into our atmosphere, since this radioactive isotope of carbon is produced when high-energy particles strike nitrogen in the atmosphere. Once linked perhaps to cosmic events like supernovae, studies have since suggested another probable cause: a monster burst of particles thrown out by the Sun. These would be generated by superflares, far bigger than anything seen in the modern era.
“They require an event that’s at least ten times bigger than anything we’ve observed,” says Mathew Owens, a space physicist at the University of Reading in the UK. The first recorded solar flare sighting dates back to the middle of the 19th Century, and are associated with the great geomagnetic storm of 1859, which has become known as the Carrington Event, after one of the astronomers who observed it, Richard Carrington.
Miyake’s discovery was confirmed by other studies of tree rings and analysis of ancient ice in cores collected from places such as Antarctica and Greenland. The latter contained correlated signatures of berylium-10 and chlorine-36, which are produced in a similar atmospheric process to carbon-14. Since then, more Miyake events, as these massive bursts of cosmic radiation and particles are now known, have been unearthed. In total, seven well studied events are known to have occurred over the past 15,000 years, while there are several other spikes in carbon-14 that have yet to be confirmed as Miyake events.
The most recent occurred just over 1,000 years ago in 993 CE. Researchers believe these events occur rarely – but at somewhat regular intervals, perhaps every 400 to 2,400 years.
The most powerful known Miyake event was discovered as recently as 2023 when Bard and his colleagues announced the discovery of a carbon-14 spike in fossilised Scots pine trees in Southern France dating back 14,300 years. The spike they saw was twice as powerful as any Miyake event seen before, suggesting these already-suspected monster events could be even bigger than previously thought.
The team behind the discovery of this superstorm from space had scoured the Southern French Alps for fossilised trees and found some that had been exposed by rivers. Using a chainsaw, they collected samples and examined them back in a laboratory, discovering evidence for an enormous carbon-14 spike. “We dreamed of finding a new Miyake event, and we were very, very happy to find this,” says Cécile Miramont, a dendrochronologist at Aix-Marseille University in France and a co-author on the study.