Archaeological methods of dating
Whenever possible, researchers use one or more absolute dating methods, which provide an age for the actual fossil or artifact.
Unlike observation-based relative dating, most absolute methods require some of the find to be destroyed by heat or other means.
Generally speaking, the more complex a poem or piece of pottery is, the more advanced it is and the later it falls in the chronology.
Egyptologists, for example, created a relative chronology of pre-pharaonic Egypt based on increasing complexity in ceramics found at burial sites.
Uranium series dating: U-series dating includes a number of methods, each based on different uranium isotopes’ decay rates.
The uranium-thorium method is often helpful for dating finds in the 40,000- to 500,000-year-old range, too old for radiocarbon but too young for K-Ar or Ar-Ar.
The good dates are confirmed using at least two different methods, ideally involving multiple independent labs for each method to cross-check results.
Researchers can measure the amount of these trapped electrons to establish an age.
The polarity is recorded by the orientation of magnetic crystals in specific kinds of rock, and researchers have established a timeline of normal and reversed periods of polarity.
Paleomagnetism is often used as a rough check of results from another dating method.
Methods fall into one of two categories: relative or absolute.
Before more precise absolute dating tools were possible, researchers used a variety of comparative approaches called relative dating.
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They then use that absolute date to establish a relative age for fossils and artifacts in relation to that layer. Anything below the Taupo tephra is earlier than 232; anything above it is later.