Have you ever walked through the forest, looked up at the trees towering above, and wondered, “How old are these trees?” I often wonder as I stare up at the canopy of branches above me. Well, there is a way to discover the age of a tree and it’s through a method called dendrochronology. I bet you didn’t know that this method of dating trees was actually invented in Arizona! There are plenty of remarkable discoveries and inventions from Arizona, and dendrochronology is one of them.

Trees hold a lot of information and history. Some trees have been around for hundreds even thousands of years while others are just a few years old. But no matter how old trees are, they are essential to our planet.
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So, how do we determine the age of a tree? Well, there's a science to it, and that science is known as dendrochronology. ("dendro" means "tree" and "chronology," as we know, is a sequence of events.)
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The science of dendrochronology was invented by Andrew Ellicott Douglass in the early 20th century. An astronomer at the Lowell Observatory, Douglass was interested in how sunspots related to the Earth's climate.
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During his research on sunspots and climate, he developed tree-ring dating. He discovered a similarity in growth patterns among trees' rings and how they could correlate to climate activity at certain points in history.
Unknown photographer/J. Connors, Who’s Who in Arizona, no. v. 1, Jo Connors, 1913/Public Domain via Wikimedia Commons
Andrew Ellicott Douglass' colleague Clark Wissler of the American Museum of Natural History in New York figured that the method of dendrochronology could also be used to date archaeological sites with prehistoric wood.
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Dendrochronology was used to give approximate dates for several ruins and sites around the Southwest.
Through tree-ring dating, we can learn more about past earthquakes, volcanic activity, and wildfires as well as the climate and the environment.
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Looking at the tree rings, a ring is one year of growth. Additionally, the wider the tree ring means there was more of a wet climate that year while a narrow tree ring means it was dry that year. I don't know about you, but I find that utterly fascinating!
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Did you know that dendrochronology was invented in Arizona? Let us know! To learn more about this method of tree-ring dating, visit the National Park Service website.

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