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Volume 84 Issue 46 | p. 14 | News of The Week
Issue Date: November 13, 2006

Ancient Teeth

Gentler laser mass spec method opens door to study of small and fragile fossils
Department: Science & Technology | Collection: Life Sciences
Tooth Tales
Deep laser-ablated test sample pits (above) on a modern rhinoceros tooth were moderated in the refined technique as indicated by the adjacent row of shallow pits. The new method was used on an ancient hominid tooth (right).
Credit: Ed King
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Tooth Tales
Deep laser-ablated test sample pits (above) on a modern rhinoceros tooth were moderated in the refined technique as indicated by the adjacent row of shallow pits. The new method was used on an ancient hominid tooth (right).
Credit: Ed King

A refined laser-ablation isotope-ratio mass spectrometry technique to study fossil tooth enamel reduces the amount of damage to rare artifacts to an acceptable level while still obtaining sufficient material for a thorough analysis (Science 2006, 314, 980). The method is anticipated to be a boon for scientists who study the diet and environment of ancient animals and prehistoric humans.

Matt Sponheimer of the University of Colorado, Boulder; Benjamin H. Passey and Thure E. Cerling of the University of Utah; and their colleagues used the method to study molars from 1.8 million-year-old early human relatives uncovered in South Africa. The data reveal that the ancient hominids ate a variable diet of seasonal fruits, leaves, and nuts from woody plants, as expected, but they also ate grains and vegetables and probably animals that fed on grasses. "We've never before been able to see dietary change within a single individual's lifetime," Sponheimer says.

The improvements came about not as a result of new technology, Passey notes, but rather as the result of trial-and-error fine-tuning to "solve a lot of nitpicky problems," such as laser power, laser pulse duration, and cryogenic trapping efficiency.

Credit: © Science
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Credit: © Science

In the technique, carbon vaporized from a sample by each laser pulse combines with oxygen to form about 20 nmol of CO2, which is whisked away from the sample chamber, purified in a cryogenic trap, and forwarded to a mass spectrometer. The researchers took multiple samples from several rows of tiny ridges on the teeth called perikymata, which are the microscopic "growth rings" of tooth enamel that form about every 10 days as teeth develop. They were able to discern the types of foods eaten by the individuals over time by the ratio of 13C to 12C in the CO2.

The researchers are "blazing a new trail" for reconstructing the diet and environment of early hominids, and their technique "should persuade museum curators to permit comprehensive surveys of isotopic variations within fossil teeth," notes Stanley H. Ambrose of the University of Illinois, Urbana-Champaign, in a commentary accompanying the Science paper.

 
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