Dendrochronology or tree-ring dating, is the scientific method of dating based on the analysis of patterns of tree rings, also known as growth rings.
In some areas of the world, it is possible to date wood back a few thousand years, or even many thousands.
In the U.S., Alexander Catlin Twining (1801-1884) suggested in 1833 that patterns among tree rings could be used to synchronize the dendrochronies of various trees and thereby to reconstruct past climates across entire regions!
Dendrochronology is a technique that ensures each individual tree ring is assigned its exact year of formation. This is accomplished by matching patterns of wide and narrow rings between cores from the same tree, and between trees from different locations.