Tree rings from ancient coffins offer clues to Earth’s past

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By Taylor Mitchell Brown, Science. 

Excerpt: About 2200 years ago, a wealthy Han soldier was entombed in a hillside grave on the frontier of the expanding Han Dynasty, in what is now western China. His tomb was filled with gold coins and emblazoned with ornate calligraphy. But what most interested Bao Yang at the Chinese Academy of Sciences (CAS) and head of its Tree-Ring Laboratory was the wood of his coffin. For dendrochronologists like Yang, coffin wood can be a critical source of tree rings, which can help scientists date sites—sometimes to precise calendar years—and offer details about the region’s environment and climate during the tree’s lifetime. The thickness of rings from the Han soldier’s pine coffin and hundreds of others like it, for example, revealed that from 270 B.C.E. to 77 C.E. average humidity levels were 18% to 34% higher than today’s, which may have allowed the western Han to expand westward into what before—and is again today—a barren desert. That insight into China’s climate more than 2000 years ago, reported in December 2024 in the Proceedings of the National Academy of Sciences, is one of many from the burgeoning study of wood in ancient coffins.... 

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