By Mindy Weisberger, CNN
(CNN) — Hundreds of unusual discs unearthed in Denmark are revealing clues into how a Stone Age population responded to a devastating volcanic eruption nearly 5,000 years ago, a new study has found.
Scientists discovered the first of these small, carved stone artifacts in 1995 at a Neolithic site called Rispebjerg on the island of Bornholm, about 112 miles (180 kilometers) southeast of Copenhagen. Because many of the discs were etched with branching rays emanating from central circles — a recognizable image of the sun — archaeologists named the objects “sun stones,” though some featured motifs resembling plants or rows of crops.
Excavations uncovered hundreds more sun stones between 2013 and 2018 at Vasagård, another Neolithic site on the island about 6.2 miles (10 kilometers) northwest of Rispebjerg. Most of the Vasagård sun stones were made of local shale. They were placed in ditches around the same time and were seemingly buried on purpose, but scientists didn’t know why.
Recently, researchers fit together clues hinting at a motive for the Vasagård burial. They examined sediments from Germany, tree rings from Germany and the western United States, and frost markers in Greenland ice cores, identifying a period of intense climate cooling around 2900 BC — the time of the sun stones’ burial. Quantities of sulfate in ice cores from Greenland and Antarctica dating to about 2910 BC suggested that this cooling followed a volcanic eruption, scientists reported January 16 in the journal Antiquity.
“It was a major eruption of a great magnitude,” comparable to the well-documented eruption of Alaska’s Okmok volcano in 43 BC that cooled the climate by about 12.6 degrees Fahrenheit (7 degrees Celsius), said lead study author Rune Iversen, an archaeologist and an associate professor at the Saxo Institute at the University of Copenhagen.
Okmok’s eruption, one of the largest of the past 2,500 years, triggered more than two years of unusual cold and erratic weather that decimated crops across the Mediterranean, leading to famine and disease. The aftermath was so devastating that it is thought to have hastened the fall of the Roman Republic and the subsequent rise of the Roman Empire, another team of scientists reported in 2020.
Though little is known about the 2900 BC eruption, it is thought to have ushered in similar hardship, suffering and death in Neolithic Denmark, Iversen told CNN.
“This climate event must definitely have been devastating for them,” he said.
This culture was not previously known for producing representational images, so the appearance of sun stones at this time hints at an unusual and highly significant event for the people of Bornholm, Iversen added.
‘An ecological disaster’
While the volcano’s location is unknown, the eruption would have spewed ash and other aerosols into the atmosphere and dimmed the sun across Northern Europe, cooling the climate and causing widespread crop failure. According to the study, Stone Age farmers who depended on the sun for their harvests may have carved solar designs on stones to acknowledge their reliance on the sun, then buried the sun stones as a type of “sacrifice” in response to the climate disruption.
Depending on when the burials happened, their actions may have been a ritual to revive the dimmed sun or a celebration of the sun’s return, the scientists reported.
“The sun stones clearly show how important the sun was in the daily life of the Stone Age peasants,” said archaeologist and historian Jeanette Varberg, a curator at the National Museum of Denmark in Copenhagen.
“Everything depended on the golden disc in the sky. They looked for it to measure the time for sowing and harvest,” said Varberg, who was not involved in the research. “The sacrificing of the small sun discs could very well be linked to an ecological disaster caused by an eruption.”
The sites on Bornholm weren’t settlements. Rather, Rispebjerg and Vasagård were both places where people gathered for community rituals. Such sites existed throughout Europe during the Neolithic period, Iversen said. At Vasagård, the ditches had been around for at least 500 years before the sun stones appeared there, according to Iversen, and all stones were found within a single layer of deposits in the ditches. This placement suggested that they were deposited during a single event.
“We started to think, OK, what could have caused that event?” Iversen said. “We had sun images, and we also had field images and maybe crop images. So we’re thinking along the lines of a natural catastrophe of some kind.”
A symbolic gesture
Once chemical analysis of ice cores had confirmed a major volcanic eruption 4,900 years ago that aligned with the timing of the sun stone burials, the next step for the researchers was to see how this eruption might have altered the climate. They found answers in ancient, fossilized trees from Germany and the United States.
In these trees, growth rings that dated back to around 2900 BC were unusually close together, suggesting a poor growing season. The scientists also found earlier studies of sediment layers from lakes in Germany’s Eifel region, noting that sunlight was greatly reduced around this time.
Communal rituals often mirror everyday habits, and Stone Age farmers on Bornholm were used to sowing seeds in plowed furrows. Carving sun stones and scattering them in ditches — as seeds were scattered in fields during planting season — may have been a symbolic gesture by the community in response to their climate troubles, “to make things grow again and make the harvest thrive and maybe even make the sun reappear,” Iversen said.
Future investigation by volcanologists could identify the unknown volcano through chemical analysis of the ancient sediments, Iversen added. But for archaeologists, connecting a volcanic eruption to the ceremonial burying of sun stones raises new questions about how Neolithic people interacted with the sun and how such interactions may have shaped human cultures, Varberg added.
“Was it only on the small island of Bornholm in the Baltic Sea that the Stone Age people sacrificed sun stones around 2900 BC? Or was the sun stone ritual part of a bigger religious movement where the sun disc was central to the Stone Age peoples beliefs?” she asked via email. “Could this be the beginning of an era of the sun, where great henges — such as Stonehenge — later became impressive sanctuaries for worship of the sun and the sky? It is indeed an intriguing thought!”
Mindy Weisberger is a science writer and media producer whose work has appeared in Live Science, Scientific American and How It Works magazine.
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