Nicolas Steno (1638-1686) was a scientist and Danish Catholic cleric who was a pioneer in both anatomy and geology. By 1659, he had decided not to accept a statement as true simply because it was written in a book, but rather to rely on his own research. He is considered the father of geology and stratigraphy by some and was (ironically enough given the stance on fossils taken by many people of Christian faith these days) beatified in 1988 by Pope John Paul II. Today he is celebrated with a Google Doodle.
Steno was not first to realise that fossils derived from long-dead organisms, his contemporaries Robert Hooke and John Ray spotted that too. However, Steno realised how fossils might have been laid down in layers. His landmark theory that the fossil record was a chronology of the creatures that lived in different eras was essential to the development of Darwin’s theory of evolution by natural selection.