Nicolas Steno

Nicolas Steno (1638–1686) was a Danish anatomist and Catholic bishop whose studies of fossils and sedimentary rocks helped establish the foundations of geology.

Fossil: A preserved remnant, impression, or trace of past life, usually found in rock. Fossils prompted Steno to explain how once-living objects could become embedded in solid rock.
Principle of superposition: In an undisturbed sequence of sedimentary layers, lower beds are older than those above them. This rule expresses Steno’s insight that successive deposits preserve an order in time.
De solido intra solidum naturaliter contento: Steno’s 1669 dissertation on solids naturally contained within other solids, including fossils and crystals. This work presents his geological principles and reasoning about fossils in rock.
Thomas Bartholin: A Danish physician and anatomist known for research on the lymphatic system. Bartholin was Steno’s teacher and an influential figure in his early medical education.
Sedimentary rock: Rock formed from accumulated sediment, or from material precipitated from water. Steno’s principles describe how sedimentary layers form and relate to one another.
Principle of original horizontality: Sediment layers are initially deposited approximately horizontally. Steno used the tilting of strata to infer that deformation occurred after deposition.
Florence: A city in central Italy that was a major center of art, science, and political power. Steno conducted influential research in Florence while connected to the Medici court.
Marcello Malpighi: An Italian physician who advanced microscopic anatomy in the seventeenth century. Malpighi shared Steno’s wider anatomical world and helped establish the study of microscopic structures.
Shark anatomy: The study of a shark’s body structure, including its jaws and teeth. Comparing shark teeth with fossil glossopetrae helped Steno recognize fossils as biological remains.
Principle of lateral continuity: Sediment layers originally extend laterally until they thin out or meet a boundary. This principle lets separated rock exposures be interpreted as parts of once-continuous layers.

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