Tree ring dating and archaeology
When one can match these tree-ring patterns across successive trees in the same locale, in overlapping fashion, chronologies can be built up—both for entire geographical regions and for sub-regions.Moreover, wood from ancient structures with known chronologies can be matched to the tree-ring data (a technique called cross-dating), and the age of the wood can thereby be determined precisely.Direct reading of tree ring chronologies is a complex science, for several reasons.First, contrary to the single-ring-per-year paradigm, alternating poor and favorable conditions, such as mid-summer droughts, can result in several rings forming in a given year.A tree-ring history whose beginning- and end-dates are not known is called a floating chronology.
However, for a precise date of the death of the tree a full sample to the edge is needed, which most trimmed timber will not provide.
It also gives data on the timing of events and rates of change in the environment (most prominently climate) and also in wood found in archaeology or works of art and architecture, such as old panel paintings.
It is also used as a check in radiocarbon dating to calibrate radiocarbon ages.
During the first half of the twentieth century, the astronomer A. Douglass founded the Laboratory of Tree-Ring Research at the University of Arizona.
Douglass sought to better understand cycles of sunspot activity and reasoned that changes in solar activity would affect climate patterns on earth, which would subsequently be recorded by tree-ring growth patterns (i.e., sunspots → climate → tree rings).