This absolute dating method is also known as dendrochronology. It is based on the fact that trees produce one growth ring each year. Narrow rings grow in cold and/or dry years, and wide rings grow in warm years with plenty of moisture.

What technique compares tree-ring growth?

Scientists put all of the visual clues to work in a technique called crossdating. This technique compares growth rings from live trees with those of much older dead trees in the same area.