Nicolas Steno

Niels Steensen (Danish: Niels Steensen; Latinized to Nicolas Steno or Nicolaus Stenonius; 1 January 1638 – 25 November 1686 [NS: 11 January 1638 – 5 December 1686]) was a Danish scientist, a pioneer in both anatomy and geology who became a Catholic bishop in his later years. He has been beatified by the Catholic Church.

Steensen was trained in the classical texts on science; however, by 1659, he seriously questioned accepted knowledge of the natural world. Importantly he questioned explanations for tear production, the idea that fossils grew in the ground and explanations of rock formation. His investigations and his subsequent conclusions on fossils and rock formation have led scholars to consider him one of the founders of modern stratigraphy and modern geology. The importance of Steensen's foundational contributions to geology may be gauged from the fact that half of the twenty papers in a 2009 miscellany volume on The Revolution in Geology from the Renaissance to the Enlightenment focus on Steensen, the "preeminent Baroque polymath and founder of modern geologic thought".

Born to a Lutheran family, Steensen converted to Catholicism in 1667. After his conversion, his interest in the natural sciences rapidly waned giving way to his interest in theology. At the beginning of 1675, he decided to become a priest. Four months later, he was ordained in the Catholic clergy on Easter Sunday in 1675.