AMS counts the quantity of C isotope is constantly formed in the upper atmosphere thanks to the effects of cosmic rays on nitrogen-14 atoms.

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There are three carbon isotopes that occur as part of the Earth's natural processes; these are carbon-12, carbon-13 and carbon-14.

The unstable nature of carbon 14 (with a precise half-life that makes it easy to measure) means it is ideal as an absolute dating method.

This new method was based on gas and liquid scintillation counting and these methods are still used today, having been demonstrated as more accurate than Libby's original method (3).

Willard Libby would receive a Nobel Prize for Chemistry in 1960.

This does not mean that we have a precise year of 3780BC, it means we then need to calibrate through other methods that will show us how atmospheric concentrations of the C isotope has changed - most typically through the dendrochronology records (tree ring data) (10).

Very old trees such as North American Bristlecone Pine are ideal for constructing long and accurate records of the state of the atmosphere.The next big step in the radiocarbon dating method would be Accelerated Mass Spectrometry which was developed in the late 1980s and published its first results in 1994 (3).This was a giant leap forward in that it offered far more accurate dates for a far smaller sample (9); this made destruction of samples a far less delicate issue to researchers, especially on artefacts such as The Shroud of Turin for which accurate dates were now possible without damaging a significant part of the artefact.The other two isotopes in comparison are more common than carbon-14 in the atmosphere but increase with the burning of fossil fuels making them less reliable for study (2); carbon-14 also increases, but its relative rarity means its increase is negligible. After this point, other Absolute Dating methods may be used.Today, the radiocarbon-14 dating method is used extensively in environmental sciences and in human sciences such as archaeology and anthropology.When the half-life was corrected in 1950, the year was taken as a base date from which to calculate all resulting dates.