Slice across a tree trunk and you’ll see a target pattern of rings. Each ring is one year of growth - a band of light wood the tree built in spring, and a band of darker, denser wood it added in late summer. Counting them tells you how old the tree is.
But the rings hold even more secrets. In warm, wet years the tree grows fast and the rings are wide. In drought, cold or insect-attack years they’re narrow. Scientists called dendrochronologists read these patterns like a barcode of past weather and even past volcanic eruptions.
By matching ring patterns from living trees to older wood found in buildings, swamps and ruins, they’ve built one continuous timeline stretching back more than 13,000 years. That means a piece of ancient wood can be dated to the exact year it was cut.
