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. With the rotation of the earth around the sun, the yearly seasons create predictable and regular changes to the climate, which in turn, affect the growth of trees. Trees grow horizontally as well as vertically every year, creating a new outer later of sapwood with each growth period. The thickness of this new ring is highly dependent on climactic changes.
When a tree is felled, time stops, and the chronological cross section is exposed. Dendrochronologists measure these rings and plot them to make a diagram of all the varying thicknesses. The samples are then compared to others from different dates, and a proper sequence is created for use in site interpretation and artefact analysis. This is called Crossdating.
It is important to note that this method of dating only provides the date for when the tree was cut down, not necessarily when it was buried. Objects can be used for many years before becoming a part of the archaeological record. All we know from the tree ring analysis is that the site or object cannot be older than a certain point. We need to look at other factors in order to get a more precise date of burial.
Unfortunately, Dendrochronology is only useful in areas that have enough climactic change to create such rings. Tropical regions don’t provide enough change for rings to grow at a consistent rate, or even at all sometimes! The sapwood- outermost layer of the wood- must also be intact in order to properly date it.
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Looking to Find Out More?
M.G.L. Baillie, A Slice Through Time: Dendrochronology and Precision Dating
E.R. Cook, L.A. Kairiukstis, Methods of Dendrochronology: Applications in the Environmental Sciences
Fritz Hans Schweingruber, Tree Rings: Basics and Applications of Dendrochronology
Constructed "with much sweat" by Dr. Henri D. Grissino-Mayer, Department of Geography, The University of Tennessee
Dieter Eckstein, Human Time in Tree Rings
Manning K, Timpson A, Colledge S, Crema ER, Edinborough K, Kerig T, and Shennan SJ. 2014. The Chronology of Culture: a Comparative Assessment of European Neolithic Dating Approaches. Antiquity 88(342):1065-1080.