''But at earlier times, the carbon dates were substantially younger than the dates we estimated by uranium-thorium analysis,'' he said.''The largest deviation, 3,500 years, was obtained for samples that are about 20,000 years old.'' One reason the group believes the uranium-thorium estimates to be more accurate than carbon dating is that they produce better matches between known changes in the Earth's orbit and changes in global glaciation. Fairbanks, a member of the Lamont-Doherty group, said that if the dates of glaciation were determined using the uranium-thorium method, the delay - and the puzzle - disappeared.In principle, any material of plant or animal origin, including textiles, wood, bones and leather, can be dated by its content of carbon 14, a radioactive form of carbon in the environment that is incorporated by all living things.Because it is radioactive, carbon 14 steadily decays into other substances.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.Scientists at the New Mexico Office of Archaeological Studies use a Low Energy Plasma Radiocarbon Sampling device on a sample of gelatin at its lab near Santa Fe.The machine is used to date artifacts by doing minimal damage to the sample.
One such indicator is the uranium-thorium dating method used by the Lamont-Doherty group.
According to carbon dating of fossil animals and plants, the spreading and receding of great ice sheets lagged behind orbital changes by several thousand years, a delay that scientists found hard to explain. The group theorizes that large errors in carbon dating result from fluctuations in the amount of carbon 14 in the air.
Changes in the Earth's magnetic field would change the deflection of cosmic-ray particles streaming toward the Earth from the Sun.
“With standard radiocarbon dating, there’s a risk of contamination of carbonates.
They have to use acids and, within that process, you lose a large part of your sample and you destroy it,” Blinman explained.