Harry Hammond Hess's work as a geologist and geophysicist led to a greater understanding of the origin of major features in the world' s oceans as well as the origin of ocean crust itself. In 1945 he performed the first sonar survey of the ocean's greatest depths, the 6.9 mile (11.0 km) deep Marianas Trench. During World War II Hess discovered the existence of guyots, flat-topped, extinct volcanoes of the deep ocean basins. He was also involved in the drilling expedition--Project Mohole--to probe the Earth's mantle. As accomplished as these tasks are, he is best remembered for his work on the spreading movement of the seafloor.

Hess graduated from Yale University in 1927, and for the next two years he worked as an exploration geologist in northern Rhodesia. In 1929 he returned to the United States and began his graduate studies at Princeton University, earning a doctoral degree in 1932. Just two years later...