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  • Laser Stimulation Reveals New Details in Fossils

Photonics.com
May 2015
LAWRENCE, Kan., May 28, 2015 — Handheld lasers can cause fossils to fluoresce, revealing complex details unseen with traditional visual enhancers such as UV light.

The approach could help paleontologists identify microfossils in soil more quickly, and even detect fake or composite specimens, according to its developers at the University of Kansas and the Burke Museum of Natural History and Culture in Washington.

"Basically you want to excite electrons in the object so it emits photons you can see," said David Burnham, preparator at the university's Biodiversity Institute & Natural History Museum. "This requires a camera filter of some kind, and that's where an orange or yellow long-pass filter is used – it takes away everything else so we can see the photons."

Microraptor skull
A microraptor skull under white light (A) shows subtle color differences. With laser stimulation (B), the bone fluoresces from differences in fossil mineralogy, indicating the skull is likely a composite. Courtesy of the University of Kansas.

The researchers first used lasers a few years ago during examination of a microraptor specimen from China, when they noticed a second fossil in the surrounding material. 

"We had a mystery fossil on the same piece," Burnham said.

The Kansas researchers contacted Thomas Kaye of the Burke Museum for help identifying it. "We sent him the specimen, and he came up with this laser technique," Burnham said.

Since then, the researchers have worked to fine-tune the identification process, often using lasers on samples from Jehol Biota, a "mother lode" of 27-million-year-old fossils unearthed in the Chinese province of Liaoning.

"There have been many dinosaurs with feathers and scales that nobody has seen before because of this locality in China, where volcanic ash has preserved fossils much like in Pompeii," Burnham said. "Tissues are preserved – not just the bones. With things like feathers, we can see details really well using lasers. If the fossils themselves won't fluoresce, the background will. We can see if a primitive feather looks like a modern feather."

Because high-end technology has become less expensive, the researchers have been able to buy medium-power, short-wavelength lasers on websites like eBay and experiment with digital photographic equipment and filters. They've developed novel uses for the lasers, such as backlighting opaque specimens to reveal detail and even finding new fossils hidden within rocks or dirt.

Feather fossil


A feather under (A) reflected light, with only barbs visible; (B) polarized light, with traces of the barbules showing; and (C) laser-stimulated fluorescence of the matrix behind carbon film. The laser backlights the feather and renders the barbules visible across the entire field of view. Courtesy of the University of Kansas.

"We're finding that a blue hand-held laser is easiest to use," Burnham said. "You can buy them at different wavelengths and energy levels – you just have to be really careful to wear protective glasses."

Techniques include silhouette illumination of carbon fibers, such as the feathers of a primitive bird; microscopic imaging of specimens fluorescing beneath the specimen surface to capture details; and in-situ analysis with minimal invasiveness, where the team analyzed the arm bracelet on the skeleton of a small girl from the mid-Holocene without removing or disturbing it, finding it was fashioned from a hippopotamus tooth.

The researchers have even developed a proof-of-concept automated fossil sorter that employs a laser beam to pick microfossils from surrounding rocks and dirt.

"The reason we collect microfossils is to find tiny little teeth, and they preserve well because they're enamel – the hardest substance the body produces," Burnham said. "You walk around, find fossils, take burlap sack, and fill it with dirt, or matrix. Before, we'd bring it back to museum and go through it with a magnifying glass, separating things by hand, one by one – mostly getting rocks. To speed this up, now we have a machine that emits laser light and pops out the teeth."

Beyond these applications, the Kansas researcher said that lasers would allow paleontologists to spot phony fossils, or specimens cobbled together from many fossils and passed off as whole. This is because bones from different places or times would have dissimilar fluorescence signals.

"It allows us to detect fakes," Burnham said. "It's been going on ever since man has been around. People are trying to make the specimen look better or more intact. Museums want pretty things, so people doctor these up to make them look better. People do it fraudulently because they're easier to sell when you make something more complete. Some artists are so good you can't tell where the real thing stops and the fake thing begins. With lasers, now we'll know."

The research was published in PLOS One (doi: 10.1371/journal.pone.0125923 [open access]).

For more information, visit www.ku.edu.



GLOSSARY
fluorescence
The emission of light or other electromagnetic radiation of longer wavelengths by a substance as a result of the absorption of some other radiation of shorter wavelengths, provided the emission continues only as long as the stimulus producing it is maintained. In other words, fluorescence is the luminescence that persists for less than about 10-8 s after excitation.
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