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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.
In some cases, the latter ratio appears to be a much more accurate gauge of age than the customary method of carbon dating, the scientists said.
The older a sample is, the less (the period of time after which half of a given sample will have decayed) is about 5,730 years, the oldest dates that can be reliably measured by this process date to around 50,000 years ago, although special preparation methods occasionally permit accurate analysis of older samples.
The idea behind radiocarbon dating is straightforward, but years of work were required to develop the technique to the point where accurate dates could be obtained.
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.
New research shows, however, that some estimates based on carbon may have erred by thousands of years.
Uranium 234, a radioactive element present in the environment, slowly decays to form thorium 230.
Using a mass spectrometer, an instrument that accelerates streams of atoms and uses magnets to sort them out according to mass and electric charge, the group has learned to measure the ratio of uranium to thorium very precisely.
But the tree ring record goes no further, so scientists have sought other indicators of age against which carbon dates can be compared.
One such indicator is the uranium-thorium dating method used by the Lamont-Doherty group.