Dendrochronology relative dating
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Dating techniques are procedures used by scientists to determine the age of rocks, fossils, or artifacts. Relative dating methods tell only if one sample is older or younger than another; absolute dating methods provide an approximate date in years. The latter have generally been available only since Many absolute dating techniques take advantage of radioactive decay , whereby a radioactive form of an element decays into a non-radioactive product at a regular rate.
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How Trees Tell Time: Dendrochronology
NPS Archeology Program: Archeology for Interpreters
The dating of remains is essential in archaeology, in order to place finds in correct relation to one another, and to understand what was present in the experience of any human being at a given time and place. Inscribed objects sometimes bear an explicit date, or preserve the name of a dated individual. In such cases, dating might seem easy. However, only a small number of objects are datable by inscriptions, and there are many specific problems with Egyptian chronology, so that even inscribed objects are rarely datable in absolute terms. In the archaeology of part-literate societies, dating may be said to operate on two levels: the absolute exactness found in political history or 'history event-by-event', and the less precise or relative chronology, as found in social and economic history, where life can be seen to change with less precision over time. The contrast might also be drawn between two 'dimensions', the historical, and the archaeological, corresponding roughly to the short-term and long-term history envisaged by Fernand Braudel.
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Dendrochronology, or 'tree ring dating' as it is often known, can provide an invaluable insight into the history of a building by revealing the year in which the timbers used in its construction were felled. It was discovered early in the 20th century that trees of the same species in the same region displayed remarkably similar ring patterns across the tree trunk and in the end grain of timber beams. Each year a tree gains another ring as it grows; the thickness of which depends on the amount of growth. In a year with ideal growing conditions, trees will produce a wider ring than in a year with poor conditions, and all the trees in the same region are likely to display the same general chronological growth pattern, despite any local ecological variations. By plotting the relative thickness of these rings in a newly felled oak of say years old, a clearly identifiable sequence of variations will emerge like a date stamp for each period.
This technique was developed during the first half of the twentieth century, originally by astronomer A. Douglass sought to better understand cycles of sunspot activity and correctly reasoned that changes in solar activity would affect climate patterns on Earth, which would subsequently be recorded by tree-ring growth patterns. The technique of dendrochronology can date tree rings in many types of wood to the exact calendar year when each ring was formed. Growth rings, also referred to as tree rings or annual rings, can be seen in a horizontal cross section cut through the trunk of a tree.