These eruptions likely cast a volcanic winter over the northern hemisphere, impacting the trees at Mount Iškoras in Norway, where the study was conducted. "Blue rings look like unfinished growth ...

Taken from a tree in Norway, this stained tree sample shows a blue ring from 1902. (Credit: Pawel Matulewski and Liliana Siekacz) Human skin isn't the only thing that can change color after facing the ...