In other words, artifacts found in the upper layers of a site will have been deposited more recently than those found in the lower layers.Cross-dating of sites, comparing geologic strata at one site with another location and extrapolating the relative ages in that manner, is still an important dating strategy used today, primarily when sites are far too old for absolute dates to have much meaning.
Increasingly better-defined methods of dating have radically enhanced our ability to address questions of cultural identity and ethnicity, as well as cultural change; an understanding of the primary methods that date the past is still critical to interpreting social process.
The facility to correlate an event or episode with an absolute point in time is crucial in solving many archaeological problems.
Stratigraphy is the oldest of the relative dating methods that archaeologists use to date things.
Stratigraphy is based on the law of superposition--like a layer cake, the lowest layers must have been formed first.
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.
The scholar most associated with the rules of stratigraphy (or law of superposition) is probably the geologist Charles Lyell.
The basis for stratigraphy seems quite intuitive today, but its applications were no less than earth-shattering to archaeological theory.
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.
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.