One of the implied assumptions in radiocarbon dating is that levels of atmospheric carbon-14 have remained constant over time.
Despite its usefulness, radiocarbon dating has a number of limitations.
First, the older the object, the less carbon-14 there is to measure.
To correct for this, scientists have compared radiocarbon dates from objects who's age is known by other means, such as artifacts from Egyptian tombs, and growth rings from ancient trees.
In this way, calibration tables have been developed that eliminate the discrepancy.
It can theoretically be used to date anything that was alive any time during the last 60,000 years or so, including charcoal from ancient fires, wood used in construction or tools, cloth, bones, seeds, and leather.
It cannot be applied to inorganic material such as stone tools or ceramic pottery.
To measure the amount of radiocarbon left in a artifact, scientists burn a small piece to convert it into carbon dioxide gas.
Radiation counters are used to detect the electrons given off by decaying Carbon-14 as it turns into nitrogen.
Both Carbon-12 and Carbon-13 are stable, but Carbon-14 decays by very weak beta decay to nitrogen-14 with a half-life of approximately 5,730 years.
After the organism dies it stops taking in new carbon.
Age determinations can also be obtained from carbonate deposits such as calcite, dissolved carbon dioxide, and carbonates in ocean, lake, and groundwater sources.