Nature: Carbon dating uses the proportion of radioactive carbon-14 in organic material to determine a sample’s age. Living organisms capture 14C from the air, but the variations in the isotope’s concentration over time require the carbon record to be calibrated against other natural calendars, such as tree rings and marine corals. However, tree rings help date samples only from the relatively recent past, and 14C levels in the ocean differ from those in the atmosphere. Now, researchers have expanded the range and accuracy of carbon dating through the use of core samples from Lake Suigetsu in Japan. The lake’s bed comprises distinct layers of sediment that have been deposited twice yearly for tens of thousands of years. By measuring the 14C concentrations in leaves trapped between the layers, Christopher Bronk Ramsey from the University of Oxford in the UK and his colleagues have compiled a direct record stretching back some 52 000 years. Although the newly recalibrated carbon clock won’t drastically affect any previously measured dates, it may help better determine the order of events and the effect of climate change on early human and Neanderthal populations.