The idea behind radiocarbon dating is straightforward, but years of work were required to develop the technique to the point where accurate dates could be obtained.

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Atmospheric nuclear weapon tests almost doubled the concentration of Radiocarbon dating, also known as the C14 dating method, is a way of telling how old something is. Plants take up atmospheric carbon dioxide by photosynthesis, and are eaten by animals, so every living thing is constantly exchanging carbon-14 with its environment as long as it lives. In 1958 Hessel de Vries showed that the concentration of carbon-14 in the atmosphere varies with time and locality.

Carbon has different isotopes, which are usually not radioactive; C is the radioactive one, its half-life, or time it takes to radioactively decay to one half its original amount, is about 5,730 years.

The thing to remember about half-life is that it is a probability.

In the example above, 500 atoms are "expected" to decay. It is just what will happen on average over the course of billions and billions of atoms.

The relatively short-lived C taken into organic matter is also slightly variable. However, under about 20,000 years the results can be compared with dendrochronology, based on tree rings.

For the most accurate work, variations are compensated by means of calibration curves.

There are three main types of radiation or radioactive decay depending on the isotope.

When isotopes are unstable they emit energy in the form of radiation.

It finally ends up as a stable isotope as the element lead. Radiation can alter the structure of cells in our bodies causing mutations which can produce cancer.

The more radiation a person is exposed to, the more dangerous it is. Despite the risks, there are a number of good ways that science has used radiation.

The method was developed by Willard Libby and his colleagues at the University of Chicago in 1949.