Dendrochronology
Simply put, dendrochronology is the dating of past events like climatic changes through study of tree ring growth. Botanists, foresters and archaeologists began using this technique during the early part of the 20th century, when it was discovered that the wide rings of certain species of trees were produced during wet years and, inversely, narrow rings during dry seasons. Each year, the tree adds a new layer of wood to its trunk, thus creating these annual rings. Hmm, do I remember reading all this in college?
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