Steno’s life was punctuated by two conversions: (1) from anatomy and medicine to geology, and (2) from Lutheran to Roman Catholic confession. Why was Steno (1638–1686) motivated to solve geological problems soon after he entered the Tuscan region of Italy? Was there any link between his scientific conversion and the religious one, which occurred almost simultaneously and produced a revolution in his life?

The origin of marine fossils found in mountains had been debated in Italy for one and a half centuries. Leonardo da Vinci (1452–1519) had already given a modern scientific explanation for the problem. Ulisse Aldrovandi (1522–1605) later tackled the problem with an experimental-taxonomic approach (his famous museum and studio), and it was he who coined the word “geology” in 1603. Italy provided spectacular exposures of rocky outcrops that must have impressed the Danish scientist who had lived in the forested north European lowlands. Since the time of Giotto and his successors, such as Mantegna, Pollaiolo, Leonardo, and Bellini, the imposing Italian landscape had stimulated the visualization of geology. Inevitably, science and art merged perfectly in the work of painter and paleontologist Agostino Scilla (1629–1700). Steno was methodologically skilled and intellectually curious and was thus open to the stimuli that Italy had to offer in order to unwittingly rediscover, after Leonardo, the principles of geology and to solve the problem of fossils. Steno’s inclination to detailed “anatomical” observation of natural objects and processes as well as his religious conversion were influenced by his acquaintance with the circle of Galileo Galilei’s (1564–1647) disciples who formed the Accademia del Cimento. They were firm Roman Catholic believers. To the inductive mild rationalist and open-minded Steno, this connection could not be dismissed, and it prepared him for changing his paradigms for the sake of consistency. This occurred when a Corpus Domini procession triggered a revelation and led to his religious conversion.