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Dendrochronology

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Tree rings - 100 year old Beech Tree

Tree rings - 100 year old Beech Tree

Astrid Geck
Definition:

Dendrochronology is the formal term for tree-ring dating, the archaeological dating method that uses the growth rings of long-lived trees as a calendar. Tree-ring dating was one of the first absolute dating method, and was invented in the early decades of the 20th century by astronomer Andrew Ellicott Douglass and archaeologist Clark Wissler.

How Dendrochronology Works

In general, during the lifetimes of trees, each year the tree grows is marked by a growth ring; the tree gains a little bit of girth each year. The width of the ring added to the outside of the tree is in part dependent on the amount of moisture available to the tree--thus trees in the same area add thin rings during dry years and thick rings during wet years. If a research can obtain a string of tree samples that overlap, a precise sequence of tree rings can be derived.

Applications

Dendrochronology is extremely precise, allowing archaeologists to name the specific year a tree was cut to make a wooden object. But, in addition, the use of dendrochronology as a backup method to radiocarbon dating allowed scientists to recognize the regular pattern in which atmospheric conditions caused radiocarbon dates to vary. Radiocarbon dates which have been corrected-or rather, calibrated-by comparison to dendrochronological records are designated by the abbreviation cal BP, or calibrated years before the present.

Over the past hundred years or so, tree ring sequences have been built all over the world, with the longest to date consisting of a 10,000 year sequence in central Europe completed on oak trees by the Hohenheim Laboratory.

Sources

A brief bibliography has been assembled for this project.

This glossary entry is part of the About.com Guide to Archaeological Dating Techniques and the Dictionary of Archaeology.

Also Known As: Tree ring dating
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