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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.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.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.The method is still a standard for cemetery studies.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.
Stratigraphy is based on the law of superposition--like a layer cake, the lowest layers must have been formed first.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.Secondly, annual rainfall is a regional climatic event, and so tree ring dates for the southwest are of no use in other regions of the world.It is certainly no exaggeration to call the invention of radiocarbon dating a revolution.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.Since the turn of the century, several methods to measure elapsed time have been discovered.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.His research culminated in proving that tree ring width varies with annual rainfall.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.