Nicolaus Steno (1638–1686) claimed that the Earth has a history that can be known by analyzing mountain strata with rules today known as Steno’s Principles of Stratigraphy. This essay argues that Steno’s research on the Earth was intrinsically related to his studies of the body. Most accounts associate Steno’s research on fossils with his dissection of a shark in the fall of 1666 in Medici Florence. Instead, the author suggests that Steno turned to the Earth after reading a manuscript about (...) fossils that contradicted his research methods. The essay shows how, exactly, Steno shifted his research and writing methods from anatomy to geology. In short, by reading Steno’s geology in light of his anatomical work, the essay presents anatomy as an influential discipline that contributed to other areas of knowledge and helped to spread the idea of laws of nature. It also problematizes the categories of seventeenth-century polymathy. (shrink)