Harry Hess

Harry Hammond Hess was born on 24 May 1906 in New York City and died of a heart attack on 25 August 1969 in Woods Hole, Massachusetts, while chairing a National Academy of Sciences meeting. He earned a geology PhD from Princeton in 1932 and joined its faculty in 1934, later chairing the Geology Department from 1950 to 1966. During the Second World War he commanded the USS Cape Johnson and used its echo-sounding equipment to map flat-topped submerged volcanic seamounts across the Pacific while the ship was underway on other business, mapping that fed directly into his postwar work. In 1962 Hess proposed the seafloor spreading hypothesis: that new oceanic crust is continuously created by molten material rising along mid-ocean ridges and then pushed outward as it cools, explaining why no ocean floor anywhere is older than about 200 million years and supplying the physical mechanism Alfred Wegener's continental drift hypothesis had lacked. The idea became one of the foundations of plate tectonics.