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Radiocarbon dating is a method for estimating the age of organic material by measuring the ratio of carbon-14 to carbon-12 present.  This technique is based on the measured concentration of carbon-14 in the atmosphere, assuming relative stability, and uses the [[half-life]] of carbon-14, which is 5568 ± 30 years.  

Radiocarbon dating is a method for estimating the age of organic material by measuring the ratio of carbon-14 to carbon-12 present.  This technique is based on the measured concentration of carbon-14 in the atmosphere, assuming relative stability, and uses the [[half-life]] of carbon-14, which is 5730 ± 40 years, however a global standard half-life of 5568 ± 30 years is often employed.  

When the age of the material is a few thousand years old, the assumptions become more important and the estimates are less reliable.  Sometimes due to atmospheric disturbances the level of carbon-14 varies.  For example, testing of [[nuclear bomb|nuclear weapons]] in the atmosphere nearly doubled the concentration of carbon-14 in the Northern Hemisphere. For this reason, other isotopes with longer half-lives are used to date objects beyond the accuracy levels of carbon-14. For instance, the decay of potassium-40 is often used to accurately date dinosaur fossils.

Due to atmospheric disturbances over the history of the earth, the natural level and distribution of carbon-14 varies over time.  For example, extremely recently in the earth's history, testing of [[nuclear bomb|nuclear weapons]] in the atmosphere has increased the concentration of carbon-14 in the Northern Hemisphere. To account for this, standard calibration curves are used to take account of chronological fluctuations, and results can be obtained which are rarely more than 700 years out.

Often concentrations of other materials such as argon can render carbon dates wildly inaccurate. Thus carbon dating cannot be considered as a definitive way of establishing the age of a given sample.

 

Other isotopes with longer half-lives can also be used to date objects- however, each method has its own drawbacks. For instance, the decay of potassium-40 is often used to complement the carbon-14 dating of [[dinosaur]] [[fossils]].