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Each year a tree adds a ring of new wood, and the width of that ring refl the conditions of the growing season. Wet years produce wide rings; drought years produce narrow ones. Because the pat is the same for every tree in a region, overlapping samples can be mat against one another, extending the record far beyond the life of any single tree. This technique, called dendroc, allows archaeologists to date wooden beams to the exact year they were c. It also gives climate scientists an annual rec of rainfall that predates written obser. The method fails, however, where seasons are not clearly sepa, since a tree that grows year-round produces no distinct bound.