Numerous comparisons of radiocarbon and dendrochronological dates have been made, and a calibration curve has been established, so that radiocarbon dates can be corrected. Provided they are adjusted, radiocarbon dates are now considered reliable as far back as 5000 B. C. Since the dendrochronological sequence extends back only as far as about 5500 B. C., no way exists at present to check radiocarbon dated from 5500 to 10,000 B. C.