The world is no stranger to solar storms. This year alone, we have been bombarded with storms; Some of these are so powerful that they have produced jaw-dropping auroras deep into the mid-latitudes.

Modern technologies ensure that little goes unnoticed. A fleet of satellites constantly monitor space weather, and scientists analyze the data and study the impact on Earth. Meanwhile, skywatchers turn their gaze and cameras skyward to capture the stunning auroras that sparkle during geomagnetic storms. What about solar storms that occurred before modern technology? If an unprecedented solar storm occurred thousands of years ago, how would we know about it?

Fortunately, ancient trees act as time capsules, silently recording Earth’s history. A team of researchers from the University of Arizona, led by Iryna Panyushkina and Timothy Jull, is solving these tree mysteries by carefully analyzing tree rings to reveal evidence of massive solar storms known as Miyake Events. These space weather events are so rare that only 6 such events have been detected in the last 14,500 years; The last of these occurred exactly between 664 and 663 BC.

We’re lucky this last Miyake incident happened so long ago, researchers say. “If these happened today, it would have devastating consequences for communication technologies,” Panyushkina said in her statement. he said.

Miyake events are a type of extreme solar activity first discovered by Japanese physicist Fusa Miyake in 2012. Collaborating with Panyushkina’s team, Miyake published research that revealed the hallmark of these events: a sharp increase in radioactive isotopes of carbon found in tree growth rings, particularly carbon-14, the report noted.

Carbon-14 is a naturally occurring form of radioactive carbon that forms in the atmosphere when cosmic radiation interacts with nitrogen. Eventually this carbon-14 reacts with oxygen to form carbon dioxide. Carbon dioxide then enters the trees through photosynthesis.

“Within a few months, carbon-14 will move from the stratosphere to the lower layers of the atmosphere, where it will be absorbed by the trees and become part of the wood as it grows,” Panyushkina said in a statement. he said.

Panyushkina and her team at the University of Arizona meticulously prepared individual tree rings from ancient wood samples collected from dead trees buried along river banks, as well as from wood excavated during archaeological excavations. Cellulose, the main component of wood, is burned to determine its radiocarbon content.

Once a radiocarbon burst is detected, researchers compare the tree ring data with other isotope bursts, such as beryllium-10, locked in ice cores pulled from glaciers and ice sheets, another notable natural time capsule. Like carbon-14, beryllium-10 is formed in the atmosphere by bombardment of solar particles; Precipitation such as rain or snow traps the isotope and locks it in the ice sheet.

“We know there is a solar storm if ice cores from both the North and South Poles show an increase in the beryllium-10 isotope in a given year, consistent with increased radiocarbon content in tree rings,” Panyushkina said in the statement. he said.

Data obtained from tree rings and ice allowed determining the date between 664 and 663 BC of the extreme Miyake solar storm, the timing of which had long eluded researchers. The study was published in the journal Communications Earth & Environment.