Some 14,300 years ago, a long-dead tree standing in what is now the French Alps recorded a message from the Sun. This information was etched in its very atoms. That day, high-energy particles bombarded Earth, dramatically altering the chemistry of the air. That chaos left an indelible mark in the tree’s rings: a sharp, sudden spike in radiocarbon.

This ancient pulse of cosmic radiation lay hidden in wood fibers for all these years. But now, scientists have decoded its meaning. The researchers claim the event was the most powerful solar particle storm ever known.

“This event establishes a new worst-case scenario,” said Kseniia Golubenko, a postdoctoral researcher at the University of Oulu in Finland and lead author of the study. “Understanding its scale is critical for evaluating the risks posed by future solar storms to modern infrastructure like satellites, power grids, and communication systems.”

A New Worst-Case Scenario

The discovery began with a piece of ancient wood, retrieved from beneath layers of glacial sediment in southwestern Europe. Its rings, each marking a year of growth, held an unusual radiocarbon signature.

These radiocarbon spikes, known as Miyake events, are rare but of great use to scientists. First described by Japanese physicist Fusa Miyake in 2012, they are caused by solar particle storms — eruptions of protons and other high-energy particles hurled from the Sun. Unlike solar flares or coronal mass ejections, these particles can pierce Earth’s magnetic field and create a global shower of radiation. When they collide with nitrogen atoms in the atmosphere, they create carbon-14, which trees then absorb during photosynthesis.

Golubenko and her colleague, Professor Ilya Usoskin, used a new model to make sense of the spike. Called SOCOL:14C-Ex, the model simulates how solar particle events would interact with Earth’s atmosphere under the frigid, glacial conditions of the Late Pleistocene.

Most previous models couldn’t account for how climate and geomagnetic conditions might alter the effects of these ancient events. “Our new model lifts the existing limitation to the Holocene and extends our ability to analyse radiocarbon data even for glacial climate conditions,” Golubenko said.

To confirm the model’s accuracy, the researchers first tested it on a better-known solar storm: the AD 775 event, until now considered the most intense in the radiocarbon record. The model passed the test, then turned to the prehistoric outlier.

What it revealed was astonishing: the 12,350 B.C.E. storm was about 18 percent stronger than the 775 event. And compared to the largest solar storm seen during the satellite era — in 2005 — it was over 500 times more intense.

What If It Happened Today?

In our own time, solar storms mostly make headlines when they generate auroras or briefly disrupt communications. The 1859 Carrington Event, one of the most powerful solar flares ever observed, caused telegraph systems to fail and sparked global auroras. But it wasn’t a solar particle event.

The kind of storm that struck in 12,350 B.C.E. belongs to a more dangerous class: extreme solar particle events (or ESPEs). Only eight such events have been identified in the past 12,000 years, including episodes in 994 A.D., 663 B.C.E., and 5259 B.C.E.

These episodes are “up to three orders of magnitude stronger” than any solar storm observed in the satellite era, according to a 2024 study. If one were to occur now — especially during a period of weakened geomagnetic shielding — the effects could be severe. We would have power outages, damaged satellites, and even biological harm to humans exposed at high altitudes.

“The ancient event in 12350 BC is the only known extreme solar particle event outside of the Holocene epoch,” said Golubenko. That means it occurred before the relatively warm, stable period that has hosted all of human civilization.

The new research underscores the need to think beyond recorded history when assessing the Sun’s potential threat. While the current solar cycle peaked in late 2024, future cycles could bring stronger activity of the kind we can’t even comprehend. Indeed, the May 2024 “Gannon” storm caused short-term disruptions to communications and navigation. It was the strongest solar storm in two decades — and that’s child’s play compared to what a storm of the magnitude seen in 13,350 B.C.E. would unleash today.

A Warning

By successfully simulating radiocarbon production under Ice Age conditions, the SOCOL:14C-Ex model opens the door to studying solar activity across vastly different epochs.

“This recent finding expands the timeline and intensity of known solar activity and sets a new upper boundary for such solar phenomena,” the study’s authors write.

In a world where the Sun looks serene, this work reveals its potential for destruction. The fusion furnace at the center of our solar system is capable of unleashing fury on a scale we are only beginning to grasp.

The findings appeared in the journal Earth and Planetary Science Letters.