Tree ring dating history
The patterns in America could not bias the work on patterns in Europe, because the specimens came from two different local climates, separated by an ocean.The scientists worked independently of one another.
Tree-ring chronologies have been extended to 10,000 years before present in this way.Because radiocarbon is everywhere the same in the atmosphere at any given time, tree rings which grew in the same year should have the same amount of radiocarbon.Furthermore, radiocarbon in the atmosphere fluctuates from year to year in a somewhat erratic fashion.The more ancient part of the chronology was constructed from oak logs preserved in peat beds, for example.The European oak chronology provided an excellent check of the American dendrochronologies. Ring-width patterns are determined by local environmental factors, such as temperature and rainfall.However, they did agree with the bristlecone chronology as far back as it could be checked by the shorter chronologies.
That is, rings of the same putative dendrochronological age were found to contain the same amount of radiocarbon, and to give the same pattern of fluctuations over time.
We could discuss the details of pattern-matching technique or the probability of error, but there is another, more quantitative way, to determine if the long tree-ring chronologies are accurate or not.
One can use the amount of radiocarbon in the individual tree rings.
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.
These measurements demonstrated the basic validity of the science of dendrochronology.