Steno Presents His Theories of Fossils and Dynamic Geology

By establishing that physical Earth indeed has a history, with geologic strata deposited by sedimentation and mountains and valleys formed by the collapse of plains, Steno explained the nature of marine fossils found far from the sea. His work may be considered the first modern form of paleontology and the first presentation of a geology of changes over time.

Summary of Event

Though the Greeks had observed the presence of petrified seashells inland and correctly concluded that the sea had once covered the land and deposited the shells, fossils posed several difficulties for the seventeenth century mind. First, no clear idea existed to explain fossils as the remains of once-living beings. The concept of “fossil” included anything buried in the earth or lying on its surface, and comprised a continuum from things clearly inorganic—such as gemstones—to things clearly resembling living organisms. [kw]Steno Presents His Theories of Fossils and Dynamic Geology (1669)
[kw]Geology, Steno Presents His Theories of Fossils and Dynamic (1669)
[kw]Dynamic Geology, Steno Presents His Theories of Fossils and (1669)
[kw]Fossils and Dynamic Geology, Steno Presents His Theories of (1669)
Science and technology;1669: Steno Presents His Theories of Fossils and Dynamic Geology[2350]
Geology;1669: Steno Presents His Theories of Fossils and Dynamic Geology[2350]
Italy;1669: Steno Presents His Theories of Fossils and Dynamic Geology[2350]
Steno, Nicolaus

Interpreting fossils as organic did not follow for several reasons. Some of these fossils had formed crystals and hence seemed to be inorganic. Another conclusion held that the resemblance of such fossils to organisms was fortuitous: They were “sports” (jokes) of nature. Moreover, that many organic fossils were of extinct, unknown species further obscured their nature. A second issue involved how to explain the formation of fossils. According to the Aristotelian view, fossils grew from seeds in the Earth; the neo-Platonic idea held that a molding force created the fossils in a web of affinities that united all parts of the universe. Neither view required the notion that the fossils resembling life forms were organic. A final difficulty arose from the location of the fossils, especially seashell forms located on mountains far from the sea. The biblical flood provided a reasonable explanation.

Whereas several authors of the sixteenth and early seventeenth centuries, including Leonardo da Vinci, argued that fossils were of organic origin, an understanding of the nature of fossils ultimately rested upon a theory of geological change. In the seventeenth century, Nicolaus Steno provided the first such theory.

Born Niels Stensen, Steno received training at the University of Copenhagen from Thomas Bartholin, Bartholin, Thomas perhaps the most famous anatomist of the day, and from his younger brother Erasmus Bartholin, Erasmus , a mathematician, physician, and Cartesian scholar. Steno received additional training in Amsterdam, at the University of Leiden, and in Paris. Having gained a reputation for his anatomical studies, Steno arrived in Florence in March, 1666, where Ferdinand II de’ Medici Ferdinand II de’ Medici , the grand duke of Tuscany, received him and appointed him to a post that provided a living. He was also elected to the Accademia del Cimento (Academy of Experiments Academy of Experiments ), founded in 1657 by Leopold de’ Medici, brother of the grand duke. The academy’s members included Francesco Redi, Redi, Francesco a physician who performed experiments to discredit spontaneous generation.

With the help of Ferdinand, Steno published in 1667 a work on the action of muscular contraction, to which he attached his findings from the dissection of the head of a shark caught in October of 1666. His examination of its teeth convinced Steno of the organic origin of fossilized shark teeth known as “tongue stones,” which he had observed in rocks during sojourns with Ferdinand. To support his theory, Steno had to argue convincingly that tongue stones had been produced in the sea and that they could not have grown in or on the Earth. One of his arguments rested on the observation that some of them had eroded and thus were quite old. He then presented an explanation that the fossils had formed in soil that was not firm and was covered with water. The soils containing the fossils thus were sediments, an image suggested perhaps by Steno’s early experience with chemical precipitates. Despite these arguments, Steno asserted that he drew no conclusions concerning the origins of the fossils.

Two years later, Steno published De solido intra solidum naturaliter contento dissertationis prodromus (1669; The Prodromus to a Dissertation Concerning Solids Naturally Contained Within Solids, 1671; better known as Prodromus
Prodromus (Steno) ), a work significant for its presentation of principles governing geologic history. A major goal was to explain how a solid—including a fossil or a crystal—could have formed within rocks. In the first part of this work, Steno argued definitively that fossilized animal and plant parts were formed in exactly the same way as the parts of living animals. He explained that the hard organic parts impressed their form on soft sediments. Furthermore, Steno noted that because fossil shells as well as fossil plants and the fossil remains of other animals resembled living species, it follows that fossils were organic. To account for the hardness of fossils, Steno suggested that the original matter had lost volatile particles or had taken on particles from its surroundings. Thus, he explained the nature and origin of the fossils.

In response to the problem of location, especially of marine fossils far from the oceans, Steno devised an explanation of the formation of geologic strata (rock layers). One of his principles stated that strata formed successively, with the lower stratum solidifying before the formation of the next stratum—the so-called principle of superposition. The original strata, laid down horizontally, could be lifted up or slipped down by the subsequent actions of fires and waters. Steno applied these principles to an explanation of Tuscan geology: the region’s geology formed first by the deposition of layers and then by the undermining of those layers by subterranean water or heat, which carved out caverns that then collapsed. The resulting valley filled with water, causing further sedimentation and collapsing layers.

According to Steno’s theory then, shells could be deposited during the first stage and wind up on mountains in a later stage. Throughout this work, however, Steno was careful to point out that his ideas did not contradict Scripture, and he incorporated the biblical flood into his scientific thought. These efforts succeeded, for the book easily gained the approval of the censors, one of whom was his friend Francesco Redi.


Steno’s work garnered a positive reception in England, where it also generated much debate. The secretary of the Royal Society of London, Henry Oldenburg, Oldenburg, Henry translated Prodromus into English, and Philosophical Transactions published reviews of Steno’s work. One difficulty with Steno’s work is the “young” age of the fossils studied, for the Tuscan fossils were only 5 million years old, while the English fossils were 300 million years old. For example, Martin Lister noted that while the fossils of Tuscany did indeed resemble living specimens, those found in the quarries of England, such as the ammonites (extinct mollusks), bore no resemblance to any known species and therefore could not be rightly considered the remains of organisms. To some, then, Steno’s theories raised the issue of extinction, a phenomenon incompatible with belief in creation by an all-good, all powerful God. The general acceptance of extinction would come more than a century later, as Prodromus was reprinted several times in the eighteenth century.

Steno’s work may be considered the first modern work on paleontology as well as the first presentation of a “dynamic” geology, or a geology of changes over time. During the eighteenth century, his theory of fossils prevailed and scholars accepted his geological principles. Another important aspect of his work involved his use of the scientific method. Like Galileo, he sought efficient causes for the phenomena he studied, that is, only immediate physical causes and not supernatural ones, and he affirmed the importance of personal observation. In his explanation of the development of fossils and gemstones, he relied on chemical and mechanical processes.

Further Reading

  • Cutler, Alan. The Seashell on the Mountaintop: A Story of Science, Sainthood, and the Humble Genius Who Discovered a New History of the Earth. New York: Dutton, 2003. A very readable account of the life of Steno, which focuses on his geological theories.
  • Dryburgh, Peter. “Nicholas Steno and the Foundations of Geology.” Edinburgh Geologist 41 (Autumn, 2003): 3-11. A brief account of Steno’s life and scientific contributions.
  • Kardel, Troels. Steno: Life, Science, Philosophy. Copenhagen, Denmark: Danish National Library of Science and Medicine, 1994. A scholarly assessment of Steno’s scientific work, focusing mainly on his anatomical studies, with some attention to his geological work and philosophy of science. Includes English translations of two anatomical works by Steno.
  • Rudwick, Martin J. S. The Meaning of Fossils: Episodes in the History of Paleontology. Chicago: University of Chicago Press, 1985. A classic treatment of fossils and paleontology from the sixteenth to the nineteenth century. Chapter 2 discusses Steno.
  • Steno, Nicolaus. The Prodromus of Nicolaus Steno’s Dissertation Concerning a Solid Body Enclosed by Process of Nature Within a Solid. Translated by John G. Winter. 1916. Reprint. New York: Hafner, 1968. A translation of the work in which Steno detailed his theory of geologic formations and presented his ideas on minerals, fossils, and other formations on Earth.

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