The first and simplest method of absolute dating is using objects with dates inscribed on them, such as coins, or objects associated with historical events or documents.For example, since each Roman emperor had his own face stamped on coins during his realm, and dates for emperor's realms are known from historical records, the date a coin was minted may be discerned by identifying the emperor depicted.
Not only that, it varies regionally, such that all trees within a specific species and region will show the same relative growth during wet years and dry years.
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.
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.
Douglass believed that solar flares affected climate, and hence the amount of growth a tree might gain in a given year.
His research culminated in proving that tree ring width varies with annual rainfall.
Seriation, on the other hand, was a stroke of genius.
First used, and likely invented by archaeologist Sir William Flinders-Petrie in 1899, seriation (or sequence dating) is based on the idea that artifacts change over time.
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.
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.