Absolute chronometric dating
It was now possible to assign a calendar date to archaeological sites in the American southwest for over 1000 years.
For more information on stratigraphy and how it is used in archaeology, see the Stratigraphy glossary entry.Dendrochronology has been extended in the American southwest to 322 BC, by adding increasingly older archaeological samples to the record.There are dendrochronological records for Europe and the Aegean, and the International Tree Ring Database has contributions from 21 different countries.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.Using local pine trees, Douglass built a 450 year record of the tree ring variability.
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.
Like tail fins on a Cadillac, artifact styles and characteristics change over time, coming into fashion, then fading in popularity. The standard graphical result of seriation is a series of "battleship curves," which are horizontal bars representing percentages plotted on a vertical axis.
Plotting several curves can allow the archaeologist to develop a relative chronology for an entire site or group of sites.
For detailed information about how seriation works, see Seriation: A Step by Step Description.
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.
Douglass believed that solar flares affected climate, and hence the amount of growth a tree might gain in a given year.