Few events of European prehistory are more important than the transition from ancient to modern humans around 40 000 years ago, a period that unfortunately lies near the limit of radiocarbon dating. This paper shows that as many as 70 per cent of the oldest radiocarbon dates in the literature may be too young, due to contamination by modern carbon. Future dates can be made more secure — and previous dates revised — using more refined methods of pre-treatment described here.
