The Usefulness of Dendrochronology to Archaeology
Dendrochronology is a technique that has been in use for most of the twentieth century. Essentially the process revolves around tree rings. In a moderate environment, trees grow by one ring each year and thus, to an extent, by examining these ring sequences, it is possible to understand the conditions in which the tree grew, year by year. The resultant pattern is then comparable with patterns from other trees found in similar areas, growing under similar circumstances; types of ring can then be assigned to specific years. As well as their importance for studying climatic and environmental development, these tree ring patterns, ( the culmination of which are called chronologies ), are particularly useful to archaeologists. By tracing the patterns from living trees back through time, it is possible to compare samples of wood that have been recovered from ancient structures with our established chronologies, and match the sequence of the rings, thus revealing the age of the sample. This is known as cross dating. In the 20's and 30's the archaeologist, Douglass used these techniques effectively, and was one of the first to do so. At Pueblo Bonito, in New Mexico he established, for the first time, absolute dates for forty-five different monuments. He also used the technique to study the effects of a significant drought that occurred from1276 -- 1299 ( as well as several others ). He was also able to look at the implications of the use of dead wood, and the re-using of other timbers.
Over the last twenty years more than six thousand years of chronologies, covering as far back as 7500 B.C. have been developed for the Balkans, the Aegean and the Near East. Ideally there will eventually be an unbroken database of chronologies from present to Neolithic, therefore enabling any finds from these areas to be dated in this manner, easily and also accurately. Clearly, the more patterns that are examined and compared within an area, the accuracy of such a database will increase. Invariably however gaps in the chronologies will exist due to matters beyond present control, yet contemporary discoveries continue to fill in these gaps. For example in the Aegean area, the millennium from 500 B.C. to 500 A.D. was not well documented in this way. However the first 500 years have now possibly been clarified somewhat due to the discovery of a 513 year ring-sequence, in box timbers found in the Comacchio shipwreck. The sequence has been cross dated with other ring chronologies, yet is also dated by archaeologists to the last few decades B.C. by the discovery of several tons of lead ingots, stamped "Agrippa." This is significant also as it shows that dendrochronology works best, not just by itself, but when complimented with other evidence.
Similarly, the actual technique itself does not rely solely on ring width analysis. This is crucial as ring growth, and consequently appearance can be affected drastically by...