Also known as carbon-14 (14C). A radioactive isotope in carbon absorbed by all living things and whose radioactive atoms decay following the death of the organism, disappearing entirely after 50,000 years. This fact means that the age of some organic (bone and coal) remains from the Upper Palaeolithic can be estimated by calculating how many carbon-14 atoms remain. This estimate is less exact as you go further back in time and also depends on fluctuations in the amount of carbon-14 in the atmosphere. For the period being studied at Étiolles, the estimate is correct to within 500 years.