Dating Subject to Error But scientists have long recognized that carbon dating is subject to error because of a variety of factors, including contamination by outside sources of carbon.
Therefore they have sought ways to calibrate and correct the carbon dating method.
Carbon 14 is thought to be mainly a product of bombardment of the atmosphere by cosmic rays, so cosmic ray intensity would affect the amount of carbon 14 in the environment at any given time.
#30,000-Year Limit The Lamont-Doherty group says uranium-thorium dating not only is more precise than carbon dating in some cases, but also can be used to date much older objects.
It is too soon to know whether the discovery will seriously upset the estimated dates of events like the arrival of human beings in the Western Hemisphere, scientists said.
But it is already clear that the carbon method of dating will have to be recalibrated and corrected in some cases.
They arrived at this conclusion by comparing age estimates obtained using two different methods - analysis of radioactive carbon in a sample and determination of the ratio of uranium to thorium in the sample.