Peter John Wyllie is a petrologist who was Professor of Geology at Caltech from 1983 until his retirement in 1999.[1] Prior to this, he held positions at the University of St Andrews (1955/6), the University of Pennsylvania (1958/9 and 1961-6), the University of Leeds (1959–1961), and the University of Chicago (1965–1983). He is well known for his many contributions to the understanding of magmatism, particularly through his work on the experimental petrology of magmas and volatiles. In the early 1970s, Wyllie wrote two widely used textbooks (The Dynamic Earth, 1971; and The Way the Earth Works, 1976) which integrated the new understanding of magmatism and plate tectonics. He is also famous for his contributions to the coverage of earth sciences in the Encyclopædia Britannica, particularly his outline of the field in Part Two of the Propædia.