A gigantic volcanic eruption some time around the year 2900 BCE may have darkened the sun, leading to freezing temperatures, crop failures, and famine across the northern hemisphere. At roughly the same time,

About 4,900 years ago, a Neolithic people on the Danish island Bornholm sacrificed hundreds of stones engraved with sun and field motifs. Archaeologists and climate scientists from the University of Copenhagen can now show that these ritual sacrifices coincided with a large volcanic eruption that made the sun disappear throughout Northern Europe.