Scientists have narrowed the date of a solar superstorm—one of just six to occur in more than 14,500 years—using ancient rings found on Russian timber samples and fossils dating back to the Iron Age.
That is according to Irina Panyushkina and Timothy Jull, both from the University of Arizona, who backed with funding from NASA, the EU, and the Hungarian government, are using carbon dating to pinpoint the last time a burst of cosmic radiation was so powerful that if it happened today, it would destroy power grids, satellites, and communication networks.
Published in Communications Earth & Environment, the two led a team of researchers who analysed tree rings for carbon-14, a naturally occurring radioactive carbon variant – thus pinpointing the only extreme solar storm event whose timing had eluded researchers.
According to Associate Professor Panyushkina, lead author, determining the precise timing of a mass solar eruption provides important data for scientists who study and develop models of the sun’s activity over time. She said Carbon-14 forms in the atmosphere due to cosmic radiation, which reacts with oxygen to form carbon dioxide.
“After a few months, carbon-14 will have travelled from the stratosphere to the lower atmosphere, where trees take it up and become part of the wood as they grow,” Panyushkina said.
Wood Central understands that extreme solar storms, known as Miyake events, were discovered in 2012. That year, Fusa Miyake, a Japanese physicist and collaborator of Panyushkina’s team, published a paper reporting the storms’ telltale signature: spikes in radioactive carbon isotopes in tree growth rings.
Miyake events occur when the sun’s electromagnetic field weakens, allowing plasma from the sun’s surface to escape into space. With the increased solar activity, protons bombard Earth’s atmosphere and trigger chemical reactions, leading to a spike in radioactive isotopes.
“Thanks to radiocarbon in tree rings, we now know that six Miyake events have happened over the past 14,500 years (in 7176 BCE, 5410 BCE, 5259 BCE, 660 BCE, 774 CE, and lastly in 993 CE),” Panyushkina said. “If they happened today, they would have cataclysmic effects on communication.”
Panyushkina used surgical knives to dissect tree rings from ancient wood samples, including dead trees buried in riverbanks and timbers excavated during archeological digs. Researchers then burned cellulose—the main component of wood—to determine the radiocarbon content.
To pinpoint whether solar storms caused the spikes, she compared tree-ring data to spikes other researchers found in a different isotope – known as beryllium-10 – locked in ice cores from glaciers and ice sheets, which, much like carbon-14, forms in the atmosphere due to an onslaught of particles from the sun: “If ice cores from the North Pole and the South Pole show a spike in the isotope beryllium-10 for a year corresponding to increased radiocarbon in tree rings, we know there was a solar storm,” Panyushkina said.
Whilst tree rings can act like ‘archivists’ in recording Miyake events, the researchers have not found evidence of a pattern in events: “Tree rings give us an idea of the magnitude of these massive storms, but we can’t detect any pattern, so it is unlikely we’ll ever be able to predict when such an event will happen,” Panyushkina said.
“Still, our paper will transform how we search and understand the carbon-14 spike signal of extreme solar proton events in tree rings. The energy from this event changes the atmosphere’s radiocarbon content and chemistry. We are trying to figure out how those short-lived and powerful events affect the Earth system.”
More information about the samples excavated for the research
Researchers used dead trees to study ancient tree rings. One of the wood samples came from a well-preserved tree from a riverbank at the Polar Urals, a mountain range in Russia. Another was an archaeological timber from an ancient larch tree. “The archaeological wood is from a small child’s [burial] chamber made of larch logs from the highlands of the Altai Mountains. It belongs to the Pazyryk culture, associated with the Siberian Scythians,” Panyushkina said.
“I worked on an archaeological project to date these burials, known as kurgans, in 2003. Local archaeologists from Novosibirsk [in Russia] excavated the cemetery, and I collected wood samples from the kurgans for dendrochronology and dating.”
- To read more, click here for the research, “The timing of the ca-660 BCE Miyake solar-proton event constrained to between 664 and 663 BCE.”
