26 Fossils
However, when he examined the shark’s teeth under a microscope, Steno was struck
by their resemblance to certain stone fossils called glossopetrae, or “tongue stones,” that
were found in rock layers throughout the coastal hills. Glossopetrae had been found and
known since the early Roman Empire. The famed Roman author Pliny the Elder thought
they were part of the moon that fell from the sky. As Steno compared his monstrous shark
teeth with glossopetrae samples, he suspected that glossopetrae not only resembled sharks’
teeth, they were sharks’ teeth.
Italian scientists scoffed that glossopetrae couldn’t be from a sea creature because they
were often found miles from the sea. Steno argued that they must have been deposited in
shallow water or mud when the ancient shark died and that these areas had somehow been
lifted up to become dry land. Others countered that glossopetrae couldn’t be teeth since
sharks’ teeth were not made of stone.
Steno expanded his study to include fossils that resembled bones and bone fragments.
When he viewed these under the microscope he was convinced that they, too, had originally
been bones, not stones. After months of study, Steno used the then new “corpuscular theory
of matter” (a forerunner of atomic theory) to argue that time and chemical action could alter
the composition of teeth and bones into stone.
Steno published his discovery and supporting evidence in 1669. In addition to proving
that fossils were really the ancient bones of living creatures, Steno investigated how these
bones came to lie in the middle of rock layers. Through this work he discovered the process
of sedimentation and of creating sedimentary rock layers. For this discovery Steno is also
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