The curve, called INTCAL09, not only extends radiocarbon calibration but also considerably improves earlier parts of the curve.
"The new radiocarbon calibration curve will be used worldwide by archaeologists and earth scientists to convert radiocarbon ages into a meaningful time scale comparable to historical dates or other estimates of calendar age," said Dr. Paula Reimer of the University of Sheffield.
"It is significant because this agreed calibration curve now extends over the entire normal range of radiocarbon dating, up to 50,000 years before today. Comparisons of the new curve to ice-core or other climate archives will provide information about changes in solar activity and ocean circulation."
It has taken nearly 30 years for researchers to produce a calibration curve this far back in time. Since the early 1980s, an international working group called INTCAL has been working on the project.
The principle of radiocarbon dating is that plants and animals absorb trace amounts of radioactive carbon-14 from carbon dioxide in the atmosphere while they are alive but stop doing so when they die. The carbon-14 decays from archaeological and geological samples so the amount left in the sample gives an indication of how old the sample is.
As the amount of carbon -14 in the atmosphere is not constant, but varies with the strength of the earth's magnetic field, solar activity and ocean radiocarbon ages must be corrected with a calibration curve.
Most experts consider the technical limit of radiocarbon dating to be about 50,000 years, after which there is too little carbon-14 left to measure accurately with present day technology.
Citation: Reimer et al., 'IntCal09 and Marine09 Radiocarbon Age Calibration Curves, 0–50,000 Years cal BP', Radiocarbon, December 2009, 51(4)