And in practice, when we cut down a tree with a known date of planting and count its rings, we can verify that they do in fact give its age.
We can also look, for example, at the timbers in an old building of known date.
And it seems very unlikely that the technique will ever take us much further.
The problem is that wood is not readily preserved; for it to last a long time, it must have been preserved under fairly unusual conditions; perhaps in an anoxic peat swamp, or buried under volcanic tuff.
This is of some interest to paleoclimatologists, but what is important from the point of view of absolute dating is that this produces a sequence of growth rings of different thicknesses which is almost as distinctive as a fingerprint.
Imagine for the sake of simplicity that there are only two thicknesses of rings: large ones and small ones.
Dendrochronologues adapt their scientific approach, their intervention and the instruments they use according to the type of object and the conservation context.
A dendrochronological study, for example, could be comprised of: - a preliminary expertise of the elements to be dated; - adapted method for sampling: core sampling, cutting or digital macro-photographs (for precious objects); - sample preparation and measuring of tree-ring widths; - synchronisation of the dendrochronological sequences of the samples; - dating of these sequences; - interpretation of the results and contextualisation.
To know that, we would have to find a piece of wood which we knew to be 10,000 years old to take the fingerprint of.When dating a wooden element, the dendrochronologue specifies, amongst other things, the geographical provenance of the used tree, allowing to reconstruct trade networks of raw materials.In addition a dendro-archaeological study allows to rediscover the old know-how of wood artisans, supplies indications concerning forest management, the selection of raw materials, etc.Now suppose we find dead wood which, unknown to us, represents growth from 1100 AD to 1600 AD.This will have a fingerprint, and the last 100 years of its fingerprint will match the first 100 years of the tree we sampled.