Radioactive dating techiques
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.
After another 5,730 years only one-quarter of the original carbon-14 will remain.
After yet another 5,730 years only one-eighth will be left.
Particular isotopes are suitable for different applications due to the type of atoms present in the mineral or other material and its approximate age.
For example, techniques based on isotopes with half lives in the thousands of years, such as Carbon-14, cannot be used to date materials that have ages on the order of billions of years, as the detectable amounts of the radioactive atoms and their decayed daughter isotopes will be too small to measure within the uncertainty of the instruments.
All rocks and minerals contain tiny amounts of these radioactive elements.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.