Steno, Nicolaus (1638–1687)

A respected anatomist, crystallographer, and priest, Nicolaus Steno (Danish: Niels Steensen) is hailed as one of the founders of modern geology. Through his dissections, laboratory experiments, and field observations, Steno was one of the first natural philosophers to recognize the organic nature of fossils and explain how sedimentary rocks were formed. His discoveries indicated that the earth has a dynamic history and is not a static body that has changed little since its formation, as was widely assumed at the time.

Born in Copenhagen in 1638, Steno was raised in a devout Lutheran household. He was a sickly youth, spending most of his formative years indoors reading science and philosophy and experimenting in his father's goldsmith shop. At the age of 18 Steno enrolled in the University of Copenhagen to study medicine but terminated his studies amidst war. He later continued his academic work in Leiden, where he earned a medical degree and set out on a successful career as an anatomist. Steno quickly became recognized as an expert on the human heart, brain, and glands. As a medical student he was the first to identify the duct of the parotid gland, which supplies saliva to the mouth. He would later impress audiences in Paris with his legendary dexterity with a scalpel, and in 1665 he published Discourse on the Anatomy of the Brain, a detailed anatomical description of the human nervous system, combined with a discussion of his philosophy of science.

In 1666 Steno traveled to Florence, where he befriended Ferdinando II de Medici, the scholarly Grand Duke of Tuscany who years earlier had established the Accademia del Cimento, the world's first academy dedicated to experimental science. Soon after his arrival, Steno was commissioned by Ferdinando to dissect the head of a giant 2,800-pound shark that landed near the port city of Livorno. In what was one of the first careful dissections of a shark, Steno noticed an uncanny resemblance between the creature's teeth and “glossopetrae,” a type of odd stone common on Malta that was thought to have curative and magical powers. Other experts had previously noted the resemblance but were at a loss to explain how petrified sharks' teeth were found on land, often on mountains thousands of feet above sea level.

Steno explained this paradox in his 1669 Prodromus to a Dissertation Concerning Solids Naturally Enclosed in Solids, now recognized as a pioneering attempt to describe the earth in terms of natural science. Noting that glossopetrae resembled modern shark teeth in every regard, Steno wrote that these odd stones must be the remains of once-living organisms. This conclusion was generalized to other fossils, such as bones and shells, and was the first coherent argument that fossils were organic. Steno also realized that since sharks are aquatic, the sediments that encased glossopetrae must have formed in the sea. Based on field excursions in Tuscany, Steno recognized that many rocks are found in layers made of [Page 1198]different materials. This observation formed the basis for Steno's Principles, three basic laws that are taught to every beginning geology student: (1) Sedimentary rocks are deposited from a fluid in originally horizontal layers; (2) in a series of layers, younger layers lie on top of older ones; and (3) sediments are deposited as laterally continuous sheets and later truncated by erosion. These principles demanded that the earth a dynamic history in which different rock layers are formed in temporal sequences, not as part of a single event such as the Biblical Flood.

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