Radiocarbon dating uses the amount of Carbon 14 (C14) available in living creatures as a measuring stick. All living things maintain a content of carbon 14 in equilibrium with that available in the atmosphere, right up to the moment of death. When an organism dies, the amount of C14 available within it begins to decay at a half life rate of 5730 years; i.e., it takes 5730 years for 1/2 of the C14 available in the organism to decay.
Comparing the amount of C14 in a dead organism to available levels in the atmosphere, produces an estimate of when that organism died. So, for example, if a tree was used as a support for a structure, the date that tree stopped living (i.e., when it was cut down) can be used to date the building's construction date.
Studies have indicated that the amount of carbon in the atmosphere has not remained constant, and beginning about 1500 BC, dates provided by radiocarbon are too recent. These dates become farther off the older the time is indicated. Calibration of radiocarbon dates to offset the error is accomplished by a fairly complicated set of formulas, but they primarily use comparison to dendrochronology dating referents.
Because of the rates of decay, radiocarbon dating is not useful for sites older than 50,000 years old. Archaeological sites older than that period must rely on alternative means of dating.
- See the article on RCYBP for more information.
- Also see Radiocarbon Calibration Update for the latest information on calibration of this essential dating method.
SourcesFor more detailed information on this and other dating techniques used in archaeology, see the Dating in Archaeology Short Course.
This glossary entry is part of the Dictionary of Archaeology.