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In 1901, Douglass began investigating tree ring growth as an indicator of solar cycles.Douglass believed that solar flares affected climate, and hence the amount of growth a tree might gain in a given year.Archaeologists use many different techniques to determine the age of a particular artifact, site, or part of a site.Two broad categories of dating or chronometric techniques that archaeologists use are called relative and absolute dating.Clark Wissler, an anthropologist researching Native American groups in the Southwest, recognized the potential for such dating, and brought Douglass subfossil wood from puebloan ruins.Unfortunately, the wood from the pueblos did not fit into Douglass's record, and over the next 12 years, they searched in vain for a connecting ring pattern, building a second prehistoric sequence of 585 years.And, outside of certain periods in our past, there simply were no chronologically dated objects, or the necessary depth and detail of history that would assist in chronologically dating civilizations.Without those, the archaeologists were in the dark as to the age of various societies. The use of tree ring data to determine chronological dates, dendrochronology, was first developed in the American southwest by astronomer Andrew Ellicott Douglass.
Dendrochronology has been extended in the American southwest to 322 BC, by adding increasingly older archaeological samples to the record.In 1929, they found a charred log near Show Low, Arizona, that connected the two patterns.It was now possible to assign a calendar date to archaeological sites in the American southwest for over 1000 years.Seriation is thought to be the first application of statistics in archaeology. The most famous seriation study was probably Deetz and Dethlefsen's study Death's Head, Cherub, Urn and Willow, on changing styles on gravestones in New England cemeteries.The method is still a standard for cemetery studies.
Secondly, annual rainfall is a regional climatic event, and so tree ring dates for the southwest are of no use in other regions of the world.