Depending on whether the horse had a browsing or grazing diet, the enamel contains different proportions of particular carbon isotopes.

A 2006 study proposes a fragmentation-recombination mechanism based on carbon isotope scrambling experiments.

Around the time the coral died, the skeletons showed changes in concentration of carbon isotopes, indicating a large algal bloom.

"The carbon isotope was only mildly elevated," he said.

The distribution of carbon isotopes will also be compared with that found in meteorites.

North Atlantic waters carry a characteristic signature in the form of relatively rich concentrations of a carbon isotope, carbon-13.

If a sample comes back below the threshold of four to one, he said, there is nothing to trigger the more sophisticated carbon isotope ratio test.

The device employs lasers whose light changes the electrical properties only of these two carbon isotopes, leaving all others undisturbed.

The next heaviest carbon isotope, carbon-13 (13C), has seven neutrons.

More precise dating based on carbon isotopes is now under way.