The technique often cannot pinpoint the date of an archeological site better than historic records, but is highly effective for precise dates when calibrated with other dating techniques such as tree-ring dating.An additional problem with carbon-14 dates from archeological sites is known as the "old wood" problem.By measuring the carbon-14 in organic material, scientists can determine the date of death of the organic matter in an artifact or ecofact.The relatively short half-life of carbon-14, 5,730 years, makes the reliable only up to about 50,000 years.Some scientists prefer the terms chronometric or calendar dating, as use of the word "absolute" implies an unwarranted certainty of accuracy.Absolute dating provides a numerical age or range in contrast with relative dating which places events in order without any measure of the age between events.One of the most widely used and well-known absolute dating techniques is carbon-14 (or radiocarbon) dating, which is used to date organic remains.This is a radiometric technique since it is based on radioactive decay.
The development of accelerator mass spectrometry (AMS) dating, which allows a date to be obtained from a very small sample, has been very useful in this regard.
It is possible, particularly in dry, desert climates, for organic materials such as from dead trees to remain in their natural state for hundreds of years before people use them as firewood or building materials, after which they become part of the archaeological record.
Thus dating that particular tree does not necessarily indicate when the fire burned or the structure was built.
Cosmic radiation entering the earth’s atmosphere produces carbon-14, and plants take in carbon-14 as they fix carbon dioxide.
Carbon-14 moves up the food chain as animals eat plants and as predators eat other animals. It takes 5,730 years for half the carbon-14 to change to nitrogen; this is the half-life of carbon-14.