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.
The scientists announced on June 6, 2008 that evidence from tree rings reveals massive wildfires as the likely cause, one of several theories proposed after the event, but dismissed as "simple and absurd." "A fire comes along and heat goes through the bark, killing the living tissue.
This is accomplished using wood specimens found preserved, for example, in historic buildings, or on the forest floor, or in peat bogs.The rings in a non-living specimen can be counted to determine the number of years the specimen spans.Mc Murry and her colleague solved a longstanding mystery by studying tree rings. Some people in New England thought judgment day was at hand.Accounts of that day, which became known as "New England's Dark Day," include mentions of midday meals by candlelight, night birds coming out to sing, flowers folding their petals, and strange behavior from animals.Tree rings are a good place to start thinking about how climate researchers get information about past climates.
In certain cases, trees can live for many hundreds of years and in an extraordinary case, like the bristlecone pine, thousands of years!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.The older parts of the chronology come from dead wood found lying on the ground near the living trees.This means that some pieces of wood in the earliest part of the chronology would have had to lie around on the ground for more than 7,000 years!This layer, or ring as seen in cross section, can be wide, recording a wet season, or narrow, recording a dry growing season.