The contamination story holds that chemicals containing modern radiocarbon adhered to or replaced ancient carbon in coal, wood, shell, collagen, or bone. Contaminated fossils might be found near geographically or stratigraphically localized contamination sources, although there are no known plausible ways to bombard underground nitrogen with the high-energy neutrons required to change it into radiocarbon.Our discoveries of radiocarbon in samples from all over the world and throughout the geologic column refute localized contamination.Samples from the past 70,000 years made of wood, charcoal, peat, bone, antler or one of many other carbonates may be dated using this technique.
Carbon-14 has a half-life of 5,730 ± 40 years, meaning that every 5,700 years or so the object loses half its carbon-14.
By examining the object's relation to layers of deposits in the area, and by comparing the object to others found at the site, archaeologists can estimate when the object arrived at the site.
Though still heavily used, relative dating is now augmented by several modern dating techniques.
But while the difficulties of single life may be intractable, the challenge of determining the age of prehistoric artifacts and fossils is greatly aided by measuring certain radioactive isotopes.
Until this century, relative dating was the only technique for identifying the age of a truly ancient object.