Lasers aren’t ready to prepare fossils
Inevitably, some bright ideas for laser-based paleontol- ogy ultimately come to naught. An intriguing example
was an effort to remove the rock encasing fossils with
pulses from a femtosecond laser.
Fossil preparation is a labor-intensive job. It may take
20 man-years to prepare a large dinosaur, or a month
or two to prepare the tiny skull of a mouse-sized mammal. Paleontologists tell horror stories of wonderful fossils
entombed in ironstone or other rock that is virtually impossible to remove without damaging or destroying the fossil.
So in 1999 when Lowell Wood of the Lawrence Livermore
National Laboratory told the annual meeting of the Society
for Vertebrate Paleontology that a laser could do the job,
scientists and fossil preparators listened eagerly.
The idea was to fire 100-fs infrared laser pulses at
the rock surface. The high peak power of the pulse
would vaporize the top micrometer of the rock. However,
because of its short duration, the laser would not damage
any underlying material. Then the laser would fire again
to remove another micrometer of rock in the small target
zone. Wood and colleagues at Livermore had shown that
sensors monitoring the spectrum of the laser-produced
plasma could discern bone from rock by detecting the
phosphorous that is abundant in bone but rare in rock. As
soon as a laser pulse vaporized a bit of phosphorous-rich
bone, the sensors would spot it and shut down the laser.
Livermore had been studying other applications of
femtosecond pulses, and Wood’s group investigated fossil application on their own time. The idea sounded great,
particularly for small fossils embedded in hard rock that
was hard to discern from the fossil. “We’ve been fantasizing for years about some kind of robot that would do
preparation,” Pete Reser, then chief preparator at the New
Mexico Museum of Natural History, told me at the time. “In
theory it could do extremely detailed preparation without
harming the specimen.” But he doubted it would prove
practical and was sure he couldn’t afford the expensive
laser system if it did.
In the end, the robotic laser system was quietly abandoned because Livermore management deemed it too far
from the lab’s main mission. At best its applications would
have been limited to small, delicate fossils in particularly
hard rock. But even then, no paleontology lab would have
had the budget to buy one. Like other paleontologists
using sophisticated instruments, they would have had to
borrow time on someone else’s equipment. —J.H.
3D dinosaur printing
Techniques for molding original fossils and casting replicas
are well developed and remain standard for making physical
copies of most fossils. “Rapid prototype printers are getting
better and better, but still a well-made mold and cast give you
a very nice crisp detail” that is not possible with a laser print,
Dallman says. ;e high cost of the special materials also makes
rapid-prototype copies more expensive than casts.
Yet 3D printing has found a niche in creating spare parts
for museum displays. A scanned image of a bone from the
right foot could be flipped and 3D printed to fill a gap in the
left foot of the fossil. Scanned bones from larger and smaller
skeletons can be scaled down or up to replace missing bones.
Dallman tells of filling in a gap in the long tail of one dinosaur by scaling the remaining tail bones to the proper size and
printing them. Laser scanning can also replicate irreplaceable
fossils that can’t be moved or are too delicate to mold, such as
the skull of the giant brachiosaurus in Berlin.
Rapid prototyping does have a big advantage in requiring only digital storage. Research Casting has a collection of
10,000 molds available for casting, so Dallman says that 3D
printing from a digital library could save lots of storage space.
Laser scanning and fossil hunting
Fossil hunting and excavation represent new frontiers for laser
scanning in paleontology.
Some fossils are notoriously hard to distinguish from the
surrounding rocks in normal light—for example, pieces of
dinosaur eggshell or tiny teeth. However, Tom Kaye of the
University of Washington’s Burke Museum has found that
ultraviolet light can make eggshell and teeth glow with a fluorescence that is easily visible in the dark. He found ultraviolet
lasers induced stronger fluorescence than lamps. “Nobody’s
tracked down all the details,” says Kaye.
He thinks the fluorescence comes from phosphate and calcite,
but the technique doesn’t work for all rock formations, presumably due to di;erences in minerals. Nonetheless, he was able
to build a simple sorting system that identified fossils by their
fluorescence and separated them from other rocks. (See his web
site at www.tomkaye.com/publications_talks.shtml for a video.)
Laser scanning o;ers a way to better record the progress
of fossil excavation. Modern paleontologists try to extract as
much information as they can from fossil sites so they can
understand the environments where the fossilized animals
lived. However, it’s hard to record every detail. Excavation
inevitably destroys the original site, says Nels Peterson, an
engineer who works part-time for Montana State University’s
Museum of the Rockies. “When you go to destroy something,
there’s this huge responsibility to make sure that you record all
the pertinent information outside of your own bias,” so others
can study the site independently. He’s been testing laser scanning to record the progression of excavations, pinpointing what
was found where, but he has yet to publish a complete report.