Generally, it is not possible to construct a complete sequence of tree rings back through the historical periods using only living trees.
Chronologies derived from living trees must be extended.
Because it reacts identically to C-12 and C-13, C-14 becomes attached to complex organic molecules through photosynthesis in plants and becomes part of their molecular makeup.
Animals eating those plants in turn absorb Carbon-14 as well as the stable isotopes.
Radiocarbon, or Carbon-14, dating is probably one of the most widely used and best known absolute dating methods. Radiocarbon dating relies on a simple natural phenomenon.
This allowed for the establishment of world-wide chronologies.
For two important reasons, this does not mean that the sample comes from 3619 BC: Many types of tree reliably lay down one tree ring every year.
The following article is abstracted from The Biblical Chronologist Volume 5, Number 1. The science of constructing chronologies from tree rings is called dendrochronology. Modern trees are known to produce one growth ring per year. (The idea that ancient trees grew more than one ring per year will be discussed below.) Therefore, by coring a living tree and counting rings from the present backwards, it is possible to determine the year in which each ring grew. The bristlecone pines in the White Mountains of California live to extremely old ages, some in excess of 4,000 years.
The University of Arizona dendrochronology lab sports a (no longer living) specimen which contains over 6,000 rings.
When plants are alive the carbon-14 to carbon-12 ratio remains constant, but after they die the ratio begins to decline.
A measurement of the ratio, therefore, provides a way to estimate how much time has elapsed since the plant was alive.