Dendrochronology is the formal term for tree-ring dating, the science that uses the growth rings of trees as a detailed record of climatic change in a region, as well as a way to approximate the date of construction for wooden objects of many types. As archaeological dating techniques go, dendrochronology is extremely precise: if the growth rings in a wooden object are preserved and can be tied into an existing chronology, researchers can determine the precise calendar year—and often season—the tree was cut down to make it. Radiocarbon dates which have been calibrated by comparison to dendrochronological records are designated by abbreviations such as cal BP, or calibrated years before the present.
Dendrochronology is a form of absolute dating that studies tree rings in order to form a chronological sequence of a specific area or region. Before radiocarbon dating came onto the field, it was one of the most reliable forms of dating for those areas that had sufficient data to create or pull from. Absolute dating methods require regular, repetitive processes that we can measure.
Dendrochronologyalso called tree-ring datingthe scientific discipline concerned with dating and interpreting past events, particularly paleoclimates and climatic trends, based on the analysis of tree rings. Samples are obtained by means of an increment borer, a simple metal tube of small diameter that can be driven into a tree to get a core extending from bark to centre. This core is split in the laboratory, the rings are counted and measured, and the sequence of rings is correlated with sequences from other cores.
This chronometric technique is the most precise dating tool available to archaeologists who work in areas where trees are particularly responsive to annual variations in precipitation, such as the American Southwest. Developed by astronomer A. Douglass in the s, dendrochronology—or tree-ring dating—involves matching the pattern of tree rings in archaeological wood samples to the pattern of tree rings in a sequence of overlapping samples extending back thousands of years.
All rights reserved. Archaeologists use dendrochronology to date a shipwreck found off the coast of Germany. Archaeologists have a group of unlikely allies: trees.
Calibration is not only done before an analysis but also on analytical results as in the case of radiocarbon dating —an analytical method that identifies the age of a material that once formed part of the biosphere by determining its carbon content and tracing its age by its radioactive decay. Carbon is a naturally occurring isotope of the element carbon. Results of carbon dating are reported in radiocarbon years, and calibration is needed to convert radiocarbon years into calendar years.
Ron Towner from the Laboratory of Tree-Ring Research at the University of Arizona explains the principles behind dendrochronology and why this dating method is valuable to archaeologists. Ron demonstrates how to accurately count tree-rings, and discusses the importance of patterns and master chronologies. Trees are often used to make analogies about the past.
Dating of archaeological timbers. Dating of period buildings. Dendrochronology or tree-ring dating is the scientific method of dating using the annual nature of tree growth in suitable tree species.
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 dendroclimatologythe study of climate and atmospheric conditions during different periods in history from wood. Dendrochronology is useful for determining the precise age of samples, especially those that are too recent for radiocarbon datingwhich always produces a range rather than an exact date, to be very accurate. However, for a precise date of the death of the tree a full sample to the edge is needed, which most trimmed timber will not provide.