Relative and chronometric dating techniques
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.
For more information on stratigraphy and how it is used in archaeology, see the Stratigraphy glossary entry.
Seriation, on the other hand, was a stroke of genius.
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.
Many of the first efforts of archaeology grew out of historical documents--for example, Schliemann looked for Homer's Troy, and Layard went after the Biblical Ninevah--and within the context of a particular site, an object clearly associated with the site and stamped with a date or other identifying clue was perfectly useful. Outside of the context of a single site or society, a coin's date is useless.
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.The scholar most associated with the rules of stratigraphy (or law of superposition) is probably the geologist Charles Lyell.In 1901, Douglass began investigating tree ring growth as an indicator of solar cycles.Douglass believed that solar flares affected climate, and hence the amount of growth a tree might gain in a given year.
For example, carbon dating is used to determine the age of organic materials.