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Using magnets to coax secrets out of fossils

March 06, 2002

Scientists continue to coax more secrets out of thunderstones and other fossils. But in order to look inside, they often have to slice their precious specimens. Magnetic resonance imaging is a non-destructive means of obtaining startling high-resolution images.

"By Thor, what`s that?!" Our ancestors must have taken fright when they came across one of the strange, long, tapered objects they called thunderstones. They believed them to be thunderbolts hurled in anger by Thor, the Norse god of thunder, or his Greek counterpart Zeus. Modern paleontology obviously knows better: Despite their sometimes impressive length of up to five meters, the belemnites were probably quite harmless when alive. Thunderstones are the fossil remains of belemnites, a anchestor of the cuttlefish, extinct during the Cretaceous period. Their scientific name is derived from the Greek word for "lightning". Traces of their fossilized remains can sometimes be seen in the marble slabs used for windowsills and flooring.

Modern evolutionary biologists would like to know more about the animals` structure and how they grew. Consequently, in their search for knowledge about life on Earth millions of years ago, they even investigate the inside of the fossils. But, cutting open a fossil destroys it. X-ray methods tend to reveal very little because looking for a stone in a stone is like looking for a white rabbit in a snowstorm. Much more promising results are provided by magnetic resonance imaging (MRI), a high-resolution, non-destructive technique that has been used in medical diagnosis on live patients and in paleontology to investigate large skeletons for many years now. But the finest resolution of which present systems are capable of is about one millimeter. This is too much for small fossils. Much finer details can be seen in the images produced by Dr. Frank Volke and Dr. Bertram Manz of the Fraunhofer Institute for Biomedical Engineering IBMT, with the participation of Albert Schaeffer (Medilan), Dr. Gabriele Gruber (Hessisches Landesmuseum in Darmstadt) and Kerstin Engel (University of Frankfurt).

"Our method opens up completely new perspectives in the non-destructive analysis of fossils," states Frank Volke, who heads the IBMT working group on magnetic resonance. "In the case of the thunderstones, we have been able to prove that tiny hydrated chalk crystals show a specific geometric orientation. This allows researchers to determine how the "bone" or internal shell of the belemnite grew. Other details visible in the 3D images are completely new and are currently being examined by experts." Frank Volke and his colleagues have submitted their results to the science journal Nature, and Professor R. Ernst, winner of the Nobel Prize for Chemistry in 1991, has lauded their work: "The experts will be excited by an additional tool which they did not consider so far in their research."

Fraunhofer-Gesellschaft