A tree' s age can be determined by counting the annual growth rings in its trunk  Each ring represents one year, and the ring' s thickness reveals the relative amount of rainfall that year  Archaeologists successfully used annual rings to determine the relative ages of ancient tombs at Pazyryk
Each tomb was constructed from freshly cut logs, and the tombs' builders were constrained by tradition to use only logs from trees growing in the sacred Pazyryk Valley
Each log in the Pazyryk tombs has among its rings a distinctive sequence of twelve annual rings representing six drought years followed by three rainy years and three more drought years.