In the year 1666, the court of the Grand Duke Ferdinando de’ Medici in Florence saw the arrival of a most unusual object—the partial carcass of a great white shark. Fishermen had caught and killed the beast off the Tuscan coast, hacked off its monstrous head, and sent the specimen at once to Ferdinando, who was an eager enthusiast of natural history. The Grand Duke’s court was the headquarters of a prestigious scientific academy and Ferdinando summoned one of its rising stars, a brilliant young anatomist from Denmark, to conduct the dissection of the shark head. His name was Nicolaus Steno.

Steno was born in 1638 in Copenhagen to a devout Lutheran family. After attending university to study medicine, he made several important anatomical discoveries in his early career before making his way to Italy where he found employment at the Medici court.

Steno was struck by the resemblance that the shark’s serrated teeth bore to the mysterious objects known as “tongue-stones.” Worn as amulets or ground into powder, tongue-stones were renowned across Europe for their alleged curative properties, reputed to heal all manner of ailments. Their origin was unclear, but several earlier thinkers had proposed that they might be petrified shark teeth. After a careful side-by-side comparison, Steno concurred.

The tongue-stones were often unearthed in rock formations alongside petrified seashells and other marine fossils, frequently miles inland, including high up in mountain ranges. How had they come to be there? Steno became determined to discover an answer. He theorized that fossiliferous strata actually started out as soft sediment laid down by the action of water, later hardening into rock and entombing the remains of organisms, which then became fossilized. Exhaustive studies of rock layers and fossils in the field only served to confirm Steno’s hypothesis.

Steno put forth his ideas in a brief abstract, De solido (On solids), enumerating three simple but brilliant principles to explain the origin and nature of sedimentary rock strata. To this day, “Steno’s Principles” can be found in any introductory geology textbook.

Superposition: In a given formation of sedimentary strata, the bottommost layer formed first, and so on in sequence, until the topmost layer, which was deposited last.

Original Horizontality: Any given sedimentary strata were originally deposited in a horizontal orientation. All apparent tilting, folding, or other deformation was produced by subsequent events.

Lateral Continuity: Corresponding strata on opposite sides of a valley or other obstruction were originally deposited as continuous layers. The obstruction was formed later.

While these principles may seem like common sense, their implication—that one rock layer could be older or younger than another—constituted a revolutionary concept in Steno’s time. Steno realized that sedimentary layers and the fossils found in them represented nothing less than a narrative history of the earth and its creatures. In a mere seventy-eight pages, Steno had laid the foundations of what would become the modern sciences of geology and paleontology.

At the same time that Steno was conducting his geological investigations, he was also undergoing a profound religious transformation. While living in Italy, the Lutheran Steno befriended many devout Catholics, and it was through discussions with them that he began to seriously consider converting to Catholicism. Steno rigorously compared the theological claims of Protestantism and Catholicism against Sacred Scripture, reading the texts in their original Hebrew and Greek. Still, he was plagued by doubts and struggled to come to a decision. Finally, on All Souls Day, 1667, Steno had a deeply personal religious experience. His doubts were dispelled, and he felt a profound certainty that God was calling him to convert to the Catholic faith. He cried out with joy: “O Lord, Thou hast broken my chains asunder!”

De solido was published in the spring of 1669 but it was to be Steno’s last great contribution to science. In the aftermath of his conversion, desire to follow the Lord wholeheartedly, Steno gave up everything in order to devote his life totally to the service of the Church. In 1675, Steno was ordained a priest. He was ordained a bishop only two years later. In 1678, the Church sent Steno to Germany. His mission there was twofold: to minister to the Catholics who remained in that country after the upheavals of the Reformation and to be a missionary among the Protestant population.

Unfortunately, Steno’s tenure in the episcopate was not as successful as his former career as a scientist. His first assignment was in Hanover, but he was soon forced to leave after a Lutheran duke came to power.  He fled to Münster, becoming an auxiliary bishop there, but his uncompromising stand against corruption in the local church made Steno many enemies in his own congregation, who forced him out. He then travelled to Hamburg where he took up an ascetic lifestyle of constant prayer, radical poverty, and physical mortification. While his admirers viewed Steno as a living saint, his radical example of holiness scandalized and offended many others. He even began to receive death threats.

Steno’s extreme penances may have fatally compromised his health. After suffering a severe abdominal ailment, Steno died on November 25, 1686, at the age of forty-eight. The late Ferdinando de’ Medici’s son, Grand Duke Cosimo, had Steno’s body returned to Florence and interred in the Basilica of San Lorenzo where it remains to this day. In 1938, the tricentenary of Steno’s birth, the cause for his canonization was officially opened at the direction of Pope Pius XI. On October 23, 1988, Nicolaus Steno was beatified by Pope St. John Paul II.

The scientific legacy of Nicolaus Steno cannot be understated. What the experiments of Gregor Mendel did for genetics and the theories of Georges Lemaître did for cosmology, Steno’s discoveries did for geology and paleontology. His famous principles laid the groundwork for our current understanding of the geological history of the earth. Because of this, he is popularly considered to be the patron saint of the geosciences. And, alongside Mendel and Lemaître, Steno’s example as a scientist and a devout Catholic provides a compelling counterargument to twenty-first century secular ideologues who declare that science and faith are incompatible. This rigid scientism presupposes a history of implacable antagonism between science and Christianity, but the fact is that there is a rich history of devout Christians, many of them Catholic, who have made outstanding contributions to the physical sciences.

There is no evidence that the Catholic Church ever took exception to Steno’s geological theories or that Steno himself ever worried that his hypotheses regarding the history of the earth and the origin of fossils might conflict with his faith. Steno’s remarkable life of science and sanctity should be an inspiration to all Catholic scientists. Blessed Nicolaus Steno, pray for us!