Relative dating stratigraphy
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.Absolute dating, the ability to attach a specific chronological date to an object or collection of objects, was a breakthrough for archaeologists.Until the 20th century, with its multiple developments, only relative dates could be determined with any confidence.The scholar most associated with the rules of stratigraphy (or law of superposition) is probably the geologist Charles Lyell.
It was now possible to assign a calendar date to archaeological sites in the American southwest for over 1000 years.
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.
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.
Determining calendar rates using dendrochronology is a matter of matching known patterns of light and dark rings to those recorded by Douglass and his successors.
Dendrochronology has been extended in the American southwest to 322 BC, by adding increasingly older archaeological samples to the record.