Carbon dating flaws dinosaurs
The Lamont-Doherty scientists conducted their analyses on samples of coral drilled from a reef off the island of Barbados.
The samples represented animals that lived at various times during the last 30,000 years. Alan Zindler, a professor of geology at Columbia University who is a member of the Lamont-Doherty research group, said age estimates using the carbon dating and uranium-thorium dating differed only slightly for the period from 9,000 years ago to the present.
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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.
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.
Carbon dating uses the radioactive decay of carbon-14 into nitrogen-14, which currently has a half-life of 5,730 years.
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 Lamont-Doherty Geological Laboratory of Columbia University at Palisades, N.
Y., reported today in the British journal Nature that some estimates of age based on carbon analyses were wrong by as much as 3,500 years.