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DUNCAN SELBY/ALAMY STOCK PHOTO

RINGS AND DATING. Dendrochronology—or counting tree rings—is one method scientists use to help calibrate radiocarbon dates. As trees are long-lived and produce one ring annually, a single tree can be used to date numerous objects and events precisely. Bristlecone pine trees (pictured here), such as the Methuselah Tree in Inyo National Forest, have one of the longest life spans of any plant. Native to the western United States, some of these hearty trees can live for 5,000 years. Their age and ability to survive in adverse conditions make the bristlecone pine perfect for use in dendrochronology.