Steno, Nicolas (1638-1686)

Danish geologist and anatomist

The son of a Copenhagen goldsmith, Nicolas Steno had a short but varied scientific career. His given name was Niels Stensen, but he is generally referred to by the Latinized version, Nicolas Steno. His name also has a variety of other spellings, such as Steensen, Stenonis (Latin), Stenone (Italian) and Stenon (French).

Steno's early schooling was accomplished in Copenhagen until 1660, when he began to travel Europe to study abroad. While a pupil of anatomy in Amsterdam, in the Netherlands, he discovered the parotid salivary duct, which is also called Stensen's duct. He made a number of other anatomical discoveries, including that muscles were made of fibrils, and he showed that the pineal gland existed in animals other than man. This was notable because some considered the pineal gland the location of the human soul, an idea first proposed by Rene Descartes (1596–1650), and so had considered it a gland unique to humans. In 1665, Steno moved to Florence, Italy, where his medical skills got him appointed physician to Grand Duke Ferdinand II of Tuscany. After returning to the Netherlands he was made Royal Anatomist in Copenhagen in 1672.

While in Italy, Steno was sent a huge shark's head that had been caught by local fishermen. While dissecting and studying it, Steno was struck by the similarity of the shark's teeth to common Mediterranean fossils known as 'tongue stones.' His study of these fossils led him to consider how any solid object could get inside another. In 1669, Steno published a short work that was to be an introduction to a larger study he never attempted, entitled De solido intra solidum naturaliter contento dissertationis prodromus (A preliminary discourse on a solid body contained naturally within a solid).

To illustrate his ideas, Steno made some of the earliest sketches of geological sections, and formulated three important geological principles. First, Steno noted that it was possible to tell which had been solid first, the rock or the fossil, by noting which was impressed on the other. In this way, Steno showed that the rocks must have formed around the fossils, and he suggested that the rocks had solidified out of former seas . Additionally, Steno argued that such rock layers would have formed in horizontal layers, and that any changes to the original horizontality must have occurred after their creation. Finally, Steno concluded that the oldest layers of rock strata must be those on the bottom, and newer layers were superposed on top of them. From this, Steno developed a geological history of rock formation, becoming one of the founders of stratigraphy .

Because the 'tongue stones' left an impression on the encasing rocks, Steno argued they had existed before the rock. Because they resembled shark's teeth so closely, he concluded that they were most likely ancient shark's teeth. Steno argued that similar fossils also had an organic origin, which went against the popular beliefs that such 'stones' had fallen from the sky, had grown from the Earth, or had more mystical origins.

Steno also made some important early studies of crystals . His observations of quartz showed that while different in appearance the quartz crystals all had the same corresponding angles between faces. He generalized this rule to all crystals, and the principle of constant angles in crystals is still known as Steno's law.

Steno had been raised a Lutheran, but in 1667, he converted to Catholicism. His faith caused him to abandon the study of science, and in 1677, he was appointed a titular bishop and spent the remainder of his days ministering to the few remaining Catholics in Northern Germany and Scandinavia.

See also Fossil record; Crystals and crystallography