Incremental dating techniques allow the construction of year-by-year annual chronologies, which can be temporally fixed (i.e., linked to the present day and thus calendar or sidereal time) or floating.
Archaeologists use tree-ring dating (dendrochronology) to determine the age of old pieces of wood. Trees usually add growth rings on a yearly basis, with the spacing of rings being wider in high growth years and narrower in low growth years. Patterns in tree-ring growth can be used to establish the age of old wood samples, and also give some hints to local climatic conditions. This technique is useful to about 9,000 years ago for samples from the western United States using overlapping tree-ring series from living and dead wood.
The science of dendrochronology is based on the phenomenon that trees usually grow by adding rings, which goes by the name of tree ring dating. Dendrochronologists date events and variations in environments in the past, analyzing and comparing growth patterns of tree rings and ancient wood. They can determine the exact calendar year each tree ring was formed.
Dendrochronological findings played an important role in early radiocarbon dating. Tree rings provided necessary material of truly known age to verify the accuracy of the carbon dating method 14. By the late 1950s, several scientists (and especially the Dutch Hessel de Vries) were able to confirm the discrepancy between the ages of radiocarbon and ages in calendar years through results obtained by carbon dating of tree rings. Tree rings were dated through dendrochronology.
Currently, tree rings continue to be used to calibrate radiocarbon determinations. Collections of tree rings of different ages are available to provide records dating back to the last 11,000 years. The most common reference trees are Pinus aristata pine, found in the USA, and Quercus sp., From Ireland and Germany. Radiocarbon dating laboratories are known to have used data from other tree species.
