The element carbon occurs in three different isotopes. While 12C and 13C are stable, 14C decays at a known rate and can therefore be used for age determination. The decay rate of 14C is known and as soon as material containing carbon (e.g. by harvesting a plant or killing an animal) is cut off from carbon exchange with the environment, the amount of the carbon isotope 14C continuously decreases. After 5,730 years, exactly half of 14C is present in the sample material, after another 5,730 years a quarter, and so on. This makes it possible to determine the age up to about 50,000 years before today.
Any material that contains 14C can be dated, from plants, wood, charcoal, bones, skin and hair, to products such as paper, cloth, leather or canvas. The same is true for carbonates such as shells, stalactites or carbonates in groundwater, oceans, rivers or lakes.
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Methods used in archaeometry can also be used to investigate biologically based materials. The main question here is not about age, but about the type of carbon source from which, for example, a fuel, oil or plastic was produced – biogenic or petrochemical (from natural gas or petroleum). These products or materials may be made from petrochemical or natural feedstocks or a mixture thereof, and can be determined using 14C analysis.
Products are called “biogenic” if their feedstocks come from natural or renewable sources, such as vegetable oils and bio-methanol. Pure petrochemical material, due to its age (the age of the petroleum from which the feedstock is derived of several million years), has carbon that does not contain 14C and has the 14C carbon signature of the corresponding year of growth of the corresponding plant.
Analyses in CEZA’s 14C laboratory can reveal these insights, and are performed according to standard test procedures ASTM-D6866 and EN-16640 respectively.