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About 2,600 years ago, ancient Assyrians witnessed a fiery red glow across the night sky. And they recorded this significant event on a stone tablet. We now know they saw bright auroras caused by a powerful solar storm. On November 20, 2024, scientists said they believe they’ve found evidence of this event in tree rings. Furthermore, they’ve pinpointed that it happened in 664 BCE, 2,688 years ago.
The researchers published their discovery in the peer-reviewed journal Communications Earth & Environment on August 23, 2024.
If a storm of that magnitude were to occur today, it would have a serious impact on our power and communications infrastructures. But it probably would not be catastrophic. Power grids and communications systems are growing increasingly resilient in weathering solar storms. To learn more, catch up with this informative interview with David Wallace, a professor of electrical engineering at Mississippi State University.
Irina Panyushkina at the University of Arizona led the team studying tree rings in ancient logs. In particular, they were measuring the amount of carbon-14 in the tree rings.
They discovered a much higher concentration of carbon-14 in rings that were formed in 664 BCE. This type of carbon-14 signature, in other studies, has been associated with solar superstorms.
What is carbon-14? It’s a type of radioactive carbon that forms continually in the atmosphere. Cosmic ray particles interact with nitrogen in the upper atmosphere to create carbon-14. Eventually, carbon-14 combines with oxygen to form carbon dioxide. Over a few months, that carbon dioxide containing carbon-14 makes its way to the lower atmosphere. There, trees take it up and store it in wood tissue.
During a solar superstorm, the sun releases enormous amounts of particles. These particles strike the Earth’s atmosphere, creating a much higher amount of carbon-14 than usual. As a result, trees alive during such an event absorb and store that additional carbon-14 in that year’s tree rings.
Scientists have identified six solar superstorms – known as Miyake events – that have happened in the past 14,500 years. They occurred in 7176 BCE, 5410 BCE, 5259 BCE, around 660 BCE, 774 CE and 993 CE.
For all Miyake events, high carbon-14 spikes were found in tree rings of ancient wood corresponding to those dates. Also, scientists have found corroborating evidence in ancient ice core samples from Greenland and Antarctica. (Higher levels of beryllium-10 and chlorine-36, found in the ice, were a result of interactions between particles from the sun during the storm and the Earth’s atmosphere.)
However, there was uncertainty about the 660 BCE event. Scientists had known, from previous tree ring data and ice core studies, that a superstorm occurred around that time, but they did not know exactly when it happened. This new study narrowed the date to 664 BCE.
When will the next solar superstorm occur? Panyushkina said:
Tree rings give us an idea of the magnitude of these massive storms, but we can’t detect any type of pattern, so it is unlikely we’ll ever be able to predict when such an event is going to happen. Still, we believe 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 type of event not only changes the atmosphere’s radiocarbon content but also the atmosphere’s chemistry. We are trying to figure out how those short-lived and powerful events affect the Earth system as a whole.
The researchers used dead trees that lived a long time ago 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. Panyushkina told EarthSky more about it:
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. 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.
Dendrochronology is the study of tree rings to date events and changes in the environment.
In temperate climates, where the seasons change, trees usually form annual rings. The size and density of each ring is determined by environmental conditions during that year. As a result, tree rings provide valuable insight into past climate in a particular region.
Tree rings can also be used for dating events. To do that, scientists build a long chronological timeline of ring patterns for a region, starting from living trees to progressively older dead trees. To date a tree ring sample, they compare the sample’s pattern to the reference chronological timeline, looking for a match. That match allows them to identify a date for their wood sample.
Bottom line: Scientists have narrowed down the date of a solar superstorm that occurred over 2,600 years ago to 664 BCE, based on a spike in carbon-14 in ancient tree rings.
Read more: Biggest solar superstorm yet, glimpsed in ancient tree rings
The post Solar superstorm in 664 BCE recorded in tree rings first appeared on EarthSky.
