There are dendrochronological records for Europe and the Aegean, and the International Tree Ring Database has contributions from 21 different countries.
The main drawback to dendrochronology is its reliance on the existence of relatively long-lived vegetation with annual growth rings.
Each tree then, contains a record of rainfall for the length of its life, expressed in density, trace element content, stable isotope composition, and intra-annual growth ring width.
Using local pine trees, Douglass built a 450 year record of the tree ring variability.
It is certainly no exaggeration to call the invention of radiocarbon dating a revolution.
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.
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.
In 1901, Douglass began investigating tree ring growth as an indicator of solar cycles.