Carbon dating of wood
Direct reading of tree ring chronologies is a complex science, for several reasons.
In 1859, the German-American Jacob Kuechler (1823–1893) used crossdating to examine oaks (Quercus stellata) in order to study the record of climate in western Texas.Dendrochronology (or tree-ring dating) is the scientific method of dating tree rings (also called growth rings) to the exact year they were formed.As well as dating them this can give data for dendroclimatology, the study of climate and atmospheric conditions during different periods in history from wood.Each ring marks a complete cycle of seasons, or one year, in the tree's life.In his Trattato della Pittura (Treatise on Painting), Leonardo da Vinci (1452–1519) was the first person to mention that trees form rings annually and that their thickness is determined by the conditions under which they grew. S., Alexander Catlin Twining (1801–1884) suggested in 1833 that patterns among tree rings could be used to synchronize the dendrochronologies of various trees and thereby to reconstruct past climates across entire regions.Hence, for the entire period of a tree's life, a year-by-year record or ring pattern builds up that reflects the age of the tree and the climatic conditions in which the tree grew.
Adequate moisture and a long growing season result in a wide ring, while a drought year may result in a very narrow one.
A tree-ring history whose beginning- and end-dates are not known is called a floating chronology.
It can be anchored by cross-matching a section against another chronology (tree-ring history) whose dates are known.
The rings are more visible in trees which have grown in temperate zones, where the seasons differ more markedly.
The inner portion of a growth ring forms early in the growing season, when growth is comparatively rapid (hence the wood is less dense) and is known as "early wood" (or "spring wood", or "late-spring wood" Many trees in temperate zones produce one growth-ring each year, with the newest adjacent to the bark.
Dendrochronologists originally carried out cross-dating by visual inspection; more recently, they have harnessed computers to do the task, applying statistical techniques to assess the matching.