The Doneraile Bone Mark
Radiocarbon years are not identical to calendar years. The concentration of radiocarbon in the atmosphere has varied through time, so laboratory determinations must be calibrated against internationally revised curves. Uncertainty becomes substantial at around 34,000 years ago. A useful local comparison comes from Derryvree, near Maguiresbridge in County Fermanagh, where roadworks exposed freshwater silts and fine sands sandwiched between two distinct tills: deposits laid down by separate advances of ice. The organic material produced a conventional radiocarbon age of 30,500 years BP, with a large error margin.