These variations, given favorable conditions, form a consistent pattern; and sections or cores taken from beams in ruins have been matched to provide a long chronology over large areas.
The central rings of this older tree may then be compared with the outer rings or a yet older tree, and so on until the dates reach back into prehistory.
Problems that arise are when climatic variation and suitable trees (sensitive trees react to climatic changes, complacent trees do not) are not be present to produce any significant and recognizable pattern of variation in the rings.
In a very dry year growth will be restricted, and the ring narrow, while a wet and humid year will produce luxuriant growth and a thick ring.
By comparing a complete series of rings from a tree of known date (for example, one still alive) with a series from an earlier, dead tree overlapping in age, ring patterns from the central layers of the recent tree and the outer of the old may show a correlation which allows the dating, in calendar years, of the older tree.
Only in a few areas of the world are there species of trees so long-lived that long chronologies can be built up.
This method is especially important in the southwestern United States, Alaska, and Scandinavia, dating back to several thousand years .
Dendrochronology, the relationship of dated ancient trees with live trees has no SYNONYMS OR RELATED TERMS: chronology CATEGORY: technique DEFINITION: The process by which an archaeologist determines dates for objects, deposits, buildings, etc., in an attempt to situate a given phenomenon in time.
, in which figures in solar years (often with some necessary margin of error) can be applied to a particular event.
A floating chronology is a decipherable record of time that was terminated long ago.