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Carbon Dating
Carbon is an element that usually contains six each of electrons, protons and neutrons. It has an isotope, carbon-14, that contains eight neutrons and is radioactive. Its half life --- the amount of time it takes for half of the carbon-14 to decay --- is 5,730 years. This figure is key to carbon dating and has been validated, helping to prove it works. Carbon-14 makes up roughly the same percentage of the bodies of all plants and animals. However, when it dies, the plant or animal no longer takes in more carbon-14 to replenish what it has lost, and the amount of the isotope decreases. As scientists have a measure of the half life of carbon-14, they can use the remaining amount to find a good estimate of an object's approximate age.
Discovery of Method
Scientists have scrutinized the accuracy of carbon dating by comparing it with other dating methods in a process known as calibration. Carbon dating was established in 1949 by scientists who used the method to date several pieces of wood with known ages. The specimens included a piece of fir tree whose age had been calculated by tree ring analysis and a piece of deck wood from an Egyptian boat whose age was known from historical documents. The ages the scientists found matched the known ages of the objects, meaning this experiment was the first proof that carbon dating works.
Importance of Calibration
Carbon dating relies on the idea that the level of carbon-14 in the atmosphere has been constant throughout history. In the 1950s, scientists realized this was not the case, and began to refine the method of carbon dating to take into account the variation in carbon-14. Calibration curves now exist and allow scientists to convert the age estimate given by carbon dating to a more accurate estimate. The curves were developed using dating techniques and give accurate results. In the course of refining carbon dating, scientists published more scientific papers proving that carbon dating works.
Restrictions
Carbon dating has restrictions and is only an accurate way to date objects containing organic matter. It cannot be used on objects over 50,000 years old, as this is much longer than the half life of carbon-14 so very little of the isotope remains in items this age or older. This means that carbon dating cannot be used on most fossils.