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C14 levels

17 September 2022

In the same issue of Current Archaeology 391 [October 2022], on page 12. ‘Science Notes‘, we have a one page report on radiocarbon dating. See https://www.archaeology.co.uk … for further information. Modern sampling, we are told, benefit from the ‘bomb curve’ – which is a large spike in atmospheric C14 coinciding with nuclear weapon testing, between 1952 and 1962. However, since reaching a peak in the mid 1960s, C14 levels have fallen. There has also been a mixing of C14 bomb period into the oceans [falling as rain] and into plants and soils, on land, leading to a declining trend in the C14/C ratio. It is claimed this trend is influenced also by the burning of fossil fuels – which are millions of years old and do not contain any C14. This is probably true as we know that plant life has responded to increasing levels of C02, by greening. They go on to claim that fossil fuel emissions into the atmosphere emit only C12 and C13 which are stable isotopes. So far so good. The argument then goes that increasing usage of fossil fuels will lead to higher levels of C02 and a lesser level of C14.

In the letters column of Nature journal, we are told, a group of scientists claimed that in 2021, measurements at La Jolla in California, and Mauna Lea in Hawaii, showed the atmospheric C14?C ratio was lower than pre-industrial levels. It has not happened, as yet, in the southern hemisphere, and the situation outside the US is not mentioned, but is expected to occur there in the next few years. Is this the latest piece of doom mongering? If it is true this means C14 is not as useful in dating as it was – in the modern period. The ration, they claim, is similar to what it was back in 1890 – making it virtually indistinguishable in age if here is not enough context to reveal they are modern samples, or not.

One is left wondering if this may have happened in the past – injections of C14 into the atmosphere, akin to the ‘bomb curve’ [rather than fossil fuel emissions}. One might wonder to what extent big volcanic explosions have on C14 dating methodology. Also, meteroric airburst phenomena have some similarities to nuclear bombs in the high atmosphere. Did they skew C14 dating? We have no idea how often these things occurred in the past. This is of course why tree rings are so useful as they help to validate C1 dates, or not.

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