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Says Shea: “Beyond 40,000 years old, the sample is so small, and the contamination risk so great, that the margin of error is thousands of years.It would be like having a watch that told you day and night.” Single crystal fusion: Also called single crystal argon or argon-argon (Ar-Ar) dating, this method is a refinement of an older approach known as potassium-argon (K-Ar) dating, which is still sometimes used.Over time, certain kinds of rocks and organic material, such as coral and teeth, are very good at trapping electrons from sunlight and cosmic rays pummeling Earth.Researchers can measure the amount of these trapped electrons to establish an age.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.The good dates are confirmed using at least two different methods, ideally involving multiple independent labs for each method to cross-check results.Sometimes only one method is possible, reducing the confidence researchers have in the results. “They’re based on ‘it’s that old because I say so,’ a popular approach by some of my older colleagues,” says Shea, laughing, “though I find I like it myself as I get more gray hair.” Kidding aside, dating a find is crucial for understanding its significance and relation to other fossils or artifacts.
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.