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In 1859, the German-American Jacob Kuechler (1823–1893) used crossdating to examine oaks (Quercus stellata) in order to study the record of climate in western Texas.
During the first half of the 20th century, the astronomer A. Douglass founded the Laboratory of Tree-Ring Research at the University of Arizona.
A tree's growth rate changes in a predictable pattern throughout the year in response to seasonal climate changes, resulting in visible growth rings.
Each ring marks a complete cycle of seasons, or one year, in the tree's life.
Instead of working with entire cross sections of trees, dendrochronologists (tree-ring researchers) often use long, slender cores extracted from trees by a hollow tool.
The diagram below shows two cores from different trees in the same area.
Dendrochronology (or tree-ring dating) is the scientific method of dating tree rings (also called growth rings) to the exact year they were formed in order to analyze atmospheric conditions during different periods in history.
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In 1929, Andrew Douglass used tree rings to accurately date archaeological ruins in the southwestern United States.
By combining data from tree ring samples at a number of locations, he was able to build a chronology, or timeline, that he then used for dating other samples.
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