The growth rings of a tree. Each ring represents one year; the outside rings, near the bark, are the youngest.

Drill for dendrochronology sampling and growth ring counting

Dendrochronology is tree-ring dating. It is a method of dating which uses the patterns of growth rings in trees. In many types of wood, the time rings were formed can be dated to the exact calendar year.

Dendrochronology has three main uses:

1. radiocarbon dating, where it is used to calibrate radiocarbon ages.
2. archaeology, where it is used to date old buildings, etc.
3. palaeoecology, where it is used to determine certain aspects of past climates

In some parts of the world, it is possible to date wood back a few thousand years, or even many thousands. The maximum for "fully anchored chronologies" is a little over 11,000 years from present. The term "fully anchored chronology" means the dates are absolutely certain.