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.Methods fall into one of two categories: relative or absolute.Various geologic, atmospheric and solar processes can influence atmospheric carbon-14 levels.Since the 1960s, scientists have started accounting for the variations by calibrating the clock against the known ages of tree rings.All ordinary matter is made up of combinations of chemical elements, each with its own atomic number, indicating the number of protons in the atomic nucleus.Additionally, elements may exist in different isotopes, with each isotope of an element differing in the number of neutrons in the nucleus.Radiometric dating is also used to date archaeological materials, including ancient artifacts.
But that assumes that the amount of carbon-14 in the atmosphere was constant — any variation would speed up or slow down the clock.
Biostratigraphy: One of the first and most basic scientific dating methods is also one of the easiest to understand.
Layers of rock build one atop another — find a fossil or artifact in one layer, and you can reasonably assume it’s older than anything above it.
Radiometric dating or radioactive dating is a technique used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed.
The method compares the abundance of a naturally occurring radioactive isotope within the material to the abundance of its decay products, which form at a known constant rate of decay.