How Do Trees Record Time?
ES2905  Natural Clocks: Using Tree Rings to Date Events

By counting back from the year a living tree was cut, it is possible to determine the date of tree rings with reasonable accuracy.

Events like fires add "marker layers" to tree rings. Because most of the trees within a limited area will show the scars from the same fires, it is possible to compare dates across several trees. This process of crossdating allows researchers to establish a timeline or chronology.

Courtesy of Laboratory of Tree-Ring Research, University of Arizona
This cross section of a tree reveals several dated fire scars. By establishing when fires occurred, researchers can date other wood samples that show a similar pattern of fire scars.
3. Other than forest fires, what else might tree rings be used to date?

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