This is an informational tour in which students gain a basic understanding of geologic time, the evidence for events in Earth’s history, relative and absolute dating techniques, and the significance of the Geologic Time Scale.Dendrochronology (or tree-ring dating) is the scientific method of dating tree rings (also called growth rings) to the exact year they were formed in order to analyze atmospheric conditions during different periods in history.
Direct reading of tree ring chronologies is a learned 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 fully anchored and cross-matched oak and pine chronology in central Europe extends back 12,460 years, Timber core samples are sampled and used to measure the width of annual growth rings; by taking samples from different sites within a particular region, researchers can build a comprehensive historical sequence.
The techniques of dendrochronology are more consistent in areas where trees grew in marginal conditions such as aridity or semi-aridity where the ring growth is more sensitive to the environment, rather than in humid areas where tree-ring growth is more uniform (complacent).
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 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 is formed 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.Diagram of secondary growth in a tree showing idealised vertical and horizontal sections.A new layer of wood is added in each growing season, thickening the stem, existing branches and roots, to form a growth ring.Cross-dating was originally done by visual inspection; more recently, computers have been harnessed to do the task, applying statistical techniques to assess the matching.