FREEING delicate fossils from the rock that has entombed them for millions of years could soon be much easier and quicker, say physicists at the Lawrence Livermore National Laboratory in California.
The researchers, who normally focus on military projects, have been working on the project in their own time. The idea is to develop a control system that switches off a cutting laser as soon as the beam slices through the surrounding rock and touches part of a fossil.
The result could be a boon to palaeontologists. At the moment, fossils have to be cleaned by hand. It is a tedious and demanding task, especially if the fossilised bones are softer than the surrounding rock. "Preparing a little mammal skull could take one to two months full time," says Pete Reser of the New Mexico Museum of Natural History, while complete dinosaurs can take up to 20 people-years.
The Livermore team uses powerful infrared laser pulses that last just 100 femtoseconds. The pulses are so short that the surface layer absorbs virtually all the energy and vaporises one micrometre at a time, leaving no excess heat behind to damage the underlying material.
To tell what the laser is cutting through, the researchers monitor the emission spectrum of the vapour produced. "We diagnosed in real time the chemistry of the material in the blow-off plume, to see if we're ablating through matrix or through bone," says Lowell Wood of Livermore. The laser is stopped as soon as phosphorus is detected, which is rare in ordinary rock but plentiful in mineralised bone. The researchersdescribed the new technique at a meeting of the Society for Vertebrate Paleontology in Denver last month.
"It would be great for micropreparation of small things, such as tiny Mesozoic mammal skulls, and really good where it was difficult to distinguish the fossil from the matrix," Reser says. The Livermore researchers have only got as far as demonstrating that the system can tell the difference between bone and rock, but next year Wood hopes to put it to work preparing fossils.
Author: Jeff Hecht
New Scientist issue 6th November 99
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