Plants, and the animals that eat them, absorb radioactive carbon-14 and stable carbon-12 from the atmosphere in proportions which – except during the atmospheric nuclear weapons tests in the 1950s and 1960s − have not changed much from the Ice Ages to the beginning of the Industrial Revolution.
When the tree dies or the animal becomes old bones, the carbon-14 decays at a predictable rate, and the ratio that remains in the laboratory sample is a measure of the specimen’s age.
“This finding has strong and, as yet, unrecognised implications for many applications of radiocarbon in various fields, and it implies that radiocarbon dating may no longer provide definitive ages for samples up to 2,000 years old.” It also could, for instance, mean that border officials may not be able to distinguish museum collection ivory from illegally-poached elephant tusks, that fraud officers will not be able to confirm the age of costly single malt whisky or vintage claret, and that Jewish and Christian scholars may no longer be able to date important historic sources such as the Dead Sea Scrolls, or resolve doubts about the much-contested provenance of iconic relics such as the Shroud of Turin.
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But Heather Graven, a lecturer in climate physics and Earth observation at Imperial College London, reports in the US journal Proceedings of the National Academy of Sciences that by 2020, as the fossil fuel emissions mount up, the fraction of carbon-14 in the atmosphere could drop to such a level that carbon-dating could become increasingly uncertain.
Fossil fuels are reservoirs of carbon from plants and algae that died so long ago that all the carbon-14 has decayed.
This made me realise that fossil fuel emissions are likely to have an impact on these various uses for radiocarbon.