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The annually formed layers of sediment from Lake Suigetsu have the potential to reveal information about environmental change in Japan over the past ∼50,000 years with chronological precision as good as, or better than, the Greenland ice cores (1). Such precision is invaluable for synchronizing records and evaluating leads and lags in the global climate system. Perhaps even more important, the fragile leaves and seeds hidden within these layers (see the figure) provide a record of past atmospheric concentration of 14C, the radioactive isotope of carbon. As reported by Bronk Ramsey et al. on page 370 of this issue (2), this record stretches back over the full length of the radiocarbon age scale. The results are invaluable for improving the accuracy with which radiocarbon dates can be converted to the calendar time scale.