The age determination of archaeological finds using radiocarbon dating could be more inaccurate than previously assumed, especially for sites in the Mediterranean. Because, as a study reveals, the growing periods of vegetation there differ from those in our latitudes. This affects the radiocarbon value and leads to falsifications of up to 50 years. This is particularly important when dating finds from ancient civilizations.
It has been the gold standard in archaeological dating since the 1940s: the measurement of carbon isotope values. “If a material is organic and old – up to 50,000 years old – you use the radiocarbon method to date it,” explains Sturt Manning from Cornell University in Ithaca.
The core of the method is the gradual decay of the carbon isotope C-14 in bones, plant remains and other organic relics over time. While living beings with water and food always absorb new amounts of this isotope generated by cosmic radiation, this replenishment does not occur with dead relics. It is therefore possible to determine from the ratio of the isotope C-14 to the stable isotope C-12 how long this carbon variant has decayed without replenishment and thus how old a fossil, the ashes of a storage bin or animal bones are.
Just a reference curve for the entire northern hemisphere
However, there is a catch: Because the production of the C-14 isotope in the atmosphere fluctuates with the intensity of the cosmic radiation reaching Earth, additional information is required. This can be obtained by analyzing certain other isotopes in the annual rings of trees. There has been a standard calibration curve for this purpose since 1986, which was determined from the annual ring data of trees of the moderate latitudes. “A single calibration curve for the northern hemisphere has been the basis for almost all radiocarbon dating in Europe and the Mediterranean for almost five decades,” explains Manning and his colleagues.
However, this reference curve does not seem to be the same in all areas, as some studies now suggest. “As the measurement accuracy increases, so do the indications of small but substantial regional deviations in the radiocarbon data of the same year,” explains Manning. Especially with remains from the Mediterranean, there are always inexplicable differences between the age that these finds should have according to historical documents or other sources and what the radiocarbon dating based on this calibration curve measures.
Deviations of up to 31 years
Manning and his team have now used systematic comparisons of wood samples from the first and second millennia BC to investigate the effect of these deviations. They compared the isotope values ​​of material from Germany with that of wood samples from Anatolia and northern Italy. The results showed that the isotope values ​​of C-14 stored in the wood show deviations in the radiocarbon dating from 13 to 31 years, even with annual rings from the same year, as the researchers report. One of the reasons for this is the fact that the C-14 content in the atmosphere also fluctuates with the growing season. In some regions of the Mediterranean, however, this is not in spring and summer as in this country, but rather in the damp and mild autumn and winter.
At first glance, a deviation of less than 50 years does not appear to be much if you consider that radiocarbon dating can go back as far as 50,000 years. However, such a deviation can provide a distorted picture, especially during the time of the high civilizations in the Mediterranean, emphasize Manning and his team. They cite the date of the death of Pharaoh Tutenchamun as an example, but also the eruption of the volcano, which largely destroyed the island of Santorini (Thera). Archaeological remains suggest that this eruption occurred around 1500 BC. Chr. Took place, but according to previous radiocarbon data it should have taken place around a hundred years earlier. Taking into account the deviations now found, Manning and his colleagues estimate a period between 1649 and 1617 – even earlier than previous measurements.
According to the scientists, it is particularly important for the research of the early cultures of the Mediterranean to recalibrate the radiocarbon dating according to the regional peculiarities. Because especially in the time around 3500 years ago – when the deviations are greatest – a lot has happened in the history of this region. “Correcting age determination could therefore also change our view of history and knowing which groups contributed to shaping classic civilizations when,” says Manning.
Source: Cornell University; Specialist article: Science Advances, doi: 10.1126 / sciadv.aaz1096