Ancient tree rings reveal largest ever solar storm 14,300 years ago

Analysis of ancient tree rings from the French Alps has revealed a massive solar storm – the largest ever identified to date – occurred about 14,300 years ago.

The clue – a spike in radiocarbon levels – was detected by an international team of scientists investigating ancient tree trunks, known as ‘subfossils’, or remains where the fossilisation process is incomplete. 

Comparing this radiocarbon spike with levels of beryllium in Greenland ice cores from the same period led the researchers to conclude the event was likely caused by a massive solar storm.

The findings are published in Royal Society’s Philosophical Transactions.

Lead author Professor Edouard Bard, at the Collège de France and multidisciplinary research centre CEREGE, says extreme solar events create short-term bursts of energetic particles that are preserved as spikes in radiocarbon.

“Radiocarbon measured in tree-rings, used alongside beryllium in polar ice cores, provide the best way to understand the Sun’s behaviour further back into the past,” he says.  

Tree rings of a buried subfossil tree in the drouzet river. Credit cecile miramont
Tree rings of a buried subfossil tree in the Drouzet river / Credit: Cécile Miramont

Extreme solar storms, called Miyake Events, are known to have occurred 9 times in the last 15,000 years. The most recent events occurred in 993AD and 774AD.

However, Miyake Events have never been directly measured, and remain poorly understood.

Bard says: “Direct instrumental measurements of solar activity only began in the 17th Century with the counting of sunspots.”

“Nowadays, we also obtain detailed records using ground-based observatories, space probes, and satellites. However, all these short-term instrumental records are insufficient for a complete understanding of the Sun,” he says.

The largest directly-observed solar storm occurred in 1859, causing massive disruption on Earth such as destroying telegraph machines.

A solar storm today on a similar scale would be catastrophic to modern technological society, potentially wiping out telecommunications, satellite systems and electricity grids, the researchers say.

The finding has potentially important implications for global communications and energy infrastructure. Better understanding such events can help humanity prepare and build resilience into these systems.

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