A tree's age can be dated to within one year by "counting" the number of these rings that a tree possesses.
However, just counting the rings may lead to an inaccurate result, because of seasonal variations in ring growth and malformations.
Instead, dendrochronologists determine the qualities of each ring and determine whether other local trees possess the same qualities in the same ring in a process called "skeleton plotting".
If the tree rings between different trees formed in a similar way, then it's likely that those trees have undergone the same variation at the same time.
Many trees in places with hot summers and cold winters make one growth ring a year.
For the entire life of a tree, a year by year record or ring pattern is formed that reveals the climate conditions in which the tree grew.
Some shells and corals also have annual growth rings.
The inner part of a growth ring is formed early in the growing season, when growth is fast and is known as early wood.
The outer portion is the late wood, and is denser than early wood.
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.