Professor of geological sciences at the University of Washington in Seattle, where he is also adjunct professor of zoology and of astronomy. Author of several books on biodiversity and the fossil record, including Rivers in Time: The Search for Clues to Earth's Mass Extinctions and Rare Earth: Why Complex Life is Uncommon in the Universe (with Donald Brownlee). He is the principal investigator for the University of Washington's portion of the NASA Astrobiology Institute.