Dating Trees by their rings
Dendrochronology (from δένδρον, dendron, "tree limb"; χρόνος, khronos, "time"; and -λογία, -logia) or tree-ring dating, is the scientific method of dating based on the analysis of patterns of tree rings, also known as growth rings. Dendrochronology can date the time at which tree rings were formed, in many types of wood, to the exact calendar year. This has three main areas of application: paleoecology, where it is used to determine certain aspects of past ecologies (most prominently climate); archaeology and the history of art and architecture, where it is used to date old panel paintings on wood, buildings, etc.; and radiocarbon dating, where it is used to calibrate radiocarbon ages (see below).
In some areas of the world, it is possible to date wood back a few thousand years, or even many thousands. Currently, the maximum for fully anchored chronologies is a little over 11,000 years from present.