14C-Dating
Dating by radiocarbon (14C) is a universally applicable dating method in archaeology and in environmental and geosciences. The method can be applied to a variety of organic materials for age determinations of up to 50,000 years before present. This and much more…
Application
Radiocarbon is present within many materials, hence all of them can be dated – from plants, wood, charcoal, bones, skin, and hair, to products such as paper, cloth, leather, and canvas.
Radiocarbon dating can also be applied to carbonates such as shells, speleothems or carbonates in groundwater, ocean water, river, and lake water. In addition, 14C-dating is applied in areas outside of archaeological research such as authenticity testing, forensics, and ivory certification (CITES). The possibility of determining the proportion of renewable (biogenic) raw materials in products of the chemical industry (e.g. biofuels and bio-oils, cosmetics, plastics) or the detection of artificial additives (e.g. aromas) in areas of the food industry, demonstrates that the application spectrum in which this method can be applied, goes far beyond dating.
The analysis of today’s atmospheric radiocarbon content reflects the usage of fossil energy (fuels, oils) and their link to climate change.
Basics
Three carbon isotopes exist in nature – 12C, 13C and 14C. The latter is radioactive and decays in the course of time. The decay rate of the 14C isotope is fixed and thus provides information on the lifespan of organic material. As soon as an organic material is cut-off from carbon exchange with the environment (e.g. by harvesting a plant or death of an animal), the amount of this carbon isotope continuously decreases. After 5,730 years, only half of the initial 14C is still present in the sample material, and after ten half-lives the remaining 14C level can no longer be detected with today’s instruments. Therefore, age determination is possible up to approx. 50,000 years (conventional 14C years) – simply by analyzing the carbon isotope ratio in a sample.
However, 14C analysis is far from „simple“, considering that the fraction of 14C is extremely low: The ratio of the isotopes 14C to 12C is only about 10-12, and in an old archaeological sample, for example, it is even smaller. One can imagine the proportion of 14C here as a single hair in relation to all the hair everyone in the world. In this case, the isotope is incredibly rare and requires extreme precision to detect.
Radiocarbon is formed in earth‘s atmosphere by the interaction of cosmic radiation with nitrogen atoms in the air. The resulting 14C immediately binds with oxygen and produces 14CO2, which then passes into plants via the process of photosynthesis. Radiocarbon then reaches humans and animals through the food chain. It is also found in rivers, oceans, soil, and sediments. An exchange between all those carbon reservoirs takes place continuously – the carbon cycle.
Limitations
The dating limit of 14C-dating is around 50,000 years (conventional 14C years), which lets us look back into the Neanderthal era. Age determinations beyond that are not possible based on radiocarbon. Much younger objects, too, can push the method to its limits: due to the large changes in the atmospheric 14C concentration between 1680 and 1950 caused by highly variable solar activity and the combustion of fossil fuels. As a result, dating with the help of 14C is ambiguous in this time period; a single radiocarbon age yields several possible calendar ages in between 1680 to 1950 after its calibration. It is therefore impossible to identify the correct calendar date that reflects the age of the object by using 14C alone.
Material formed after 1950 is influenced by man-made 14C, which was produced in the atmosphere during the nuclear-weapons tests in the 1960s. In this case, however, it is potentially possible to date samples with very high precision down to a few years. The method also impresses with its high precision in other respects: in Holocene samples (younger than 10,000 years), for example, it is generally in the range of 0.2 to 0.3 % equivalent to ± 25 to 30 radiocarbon years.