As a volcanic eruption darkened the sun roughly 4,900 years ago, a Stone Age culture sacrificed hundreds of decorated stone plaques to try to coax it back.
A trove of engraved stones unearthed from ritual gathering sites on Bornholm, an island in Denmark, display motifs that most commonly represent the sun and croplike plants. What’s more, an analysis of ice cores points to a volcanic eruption around the time the stones were intentionally buried. Taken together, the evidence suggests the stones’ burial may have been linked to the potentially cataclysmic event, archaeologist Rune Iversen and colleagues report January 15 in Antiquity.
“The predominance of sun and plant motifs is striking,” says Alison Sheridan, an archaeologist at National Museums Scotland in Edinburgh who was not involved in the research. “These stones are seen as a kind of prayer or invocation for the sun to return, and for crops to grow again.”
Iversen’s team discovered the collection of over 600 decorated stones between 2013 and 2018, in ritual gathering sites thought to have been built by the Funnel Beaker culture. These people appear to have carved out and refilled several ditches over about a century. Around 2900 B.C., they scattered sun stones across the land like seeds in a field, sealed the ditches and built several circular wooden structures on top.
“It is a bit special that all of a sudden we have all these stones, and you don’t see them from before or later,” says Iversen, of the University of Copenhagen. This led Iversen’s team to conclude the burial was in response to a major incident.
After ruling out solar eclipses, the researchers turned to ice cores from Greenland and Antarctica, which show traces of a volcanic eruption around 2910 B.C. that would have probably caused global cooling and affected harvests. Lake sediments from Germany also hint at drastically reduced sunlight around this time, while tree rings from Germany and the United States suggest several incidents of frost during growth seasons.
“The assemblage is indeed exceptional in terms of quality and quantity,” says archaeologist Marc Vander Linden of Bournemouth University in England. But he is cautious about a causal link between the burials and volcanic activity. “A priority would be to look at a much larger chronological window, to see if this period presents a specific environmental signature such as a higher incidence of colder snaps.”
It’s unclear which volcano erupted, though finding its location could shed light on its broader impact, Iversen says. The timing of the deposit coincides with the dwindling of the Funnel Beaker culture and widespread social upheaval across Europe.
“Given that the effects of the volcanic activity will have been felt over much of the Northern Hemisphere,” Sheridan says, “this makes one wonder what other reactions there may have been to it elsewhere.”
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