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Compared to conventional radiocarbon techniques such as Libby's solid carbon counting, the gas counting method popular in the mid-1950s, or liquid scintillation (LS) counting, AMS permitted the dating of much smaller sized samples with even greater precision.Regardless of the particular 14C technique used, the value of this tool for archaeology has clearly been appreciated.Radiocarbon dating is especially good for determining the age of sites occupied within the last 26,000 years or so (but has the potential for sites over 50,000), can be used on carbon-based materials (organic or inorganic), and can be accurate to within ±30-50 years.Probably the most important factor to consider when using radiocarbon dating is if external factors, whether through artificial contamination, animal disturbance, or human negligence, contributed to any errors in the determinations.Most carbon on Earth exists as the very stable isotope carbon-12, with a very small amount as carbon-13.Carbon-14 is an unstable isotope of carbon that will eventually decay at a known rate to become carbon-12.Bottom line: is a technique used by scientists to learn the ages of biological specimens – for example, wooden archaeological artifacts or ancient human remains – from the distant past.
Atoms of the same element that have different numbers of neutrons are called isotopes.As we mentioned above, the carbon-14 to carbon-12 ratio in the atmosphere remains nearly constant.It’s not absolutely constant due to several variables that affect the levels of cosmic rays reaching the atmosphere, such as the fluctuating strength of the Earth’s magnetic field, solar cycles that influence the amount of cosmic rays entering the solar system, climatic changes, and human activities.But when gas exchange is stopped, be it in a particular part of the body like in deposits on bones and teeth, or when the entire organism dies, the ratio of carbon-14 to carbon-12 begins to decrease.The unstable carbon-14 gradually decays to carbon-12 at a steady rate. Scientists measure the ratio of carbon isotopes to be able to estimate how far back in time a biological sample was active or alive.
Cosmic rays – high energy particles from beyond the solar system – bombard Earth’s upper atmosphere continually, in the process creating the unstable carbon-14. Because it’s unstable, carbon-14 will eventually decay back to carbon-12 isotopes.