Charles Marshall’s childhood passion led him to a career in paleontology, trying to understand the interplay between inheritance, environment, and catastrophe in directing evolution. Marshall’s work attracted media attention in 1996. He and University of Washington geologist Peter Ward concluded there may have been other causes than just the well-publicized comet or asteroid impact responsible for the extinctions at the end of the Cretaceous Period, when all living dinosaur species died out. Marshall used a statistical analysis of the fossil record to conclude that a major drop in sea level – preceding the impact by 150,000 to 300,000 years – may have led to as much as 25 percent of the huge number of extinctions that took place. Another 25 percent of the extinctions, the pair theorized, were so-called “background” extinctions and would have happened without the impact or the drop in sea level.