Hess, Harry Hammond (1906-1969)

Hess, Harry Hammond (1906-1969)

American geologist

Harry Hammond Hess spent much of his career studying what the ocean floor was made of and where it came from. He was a renowned geologist whose interests and influence ranged from oceanography to space science. One of Hess's most important contributions to science was the concept of seafloor spreading, which became a cornerstone in the acceptance of the continental drift theory during the 1960s. As an officer in the United States Naval Reserve, he was able to combine military service with scientific investigation; in his later years, he became an important figure in NASA, helping direct the science of lunar exploration.

Hess was born in New York City to Julian S. Hess, a member of the New York Stock Exchange, and Elizabeth Engel Hess. He attended Asbury Park High School in New Jersey before entering Yale University in 1923. At Yale, he intended to study electrical engineering, but changed his mind and graduated in 1927 with a B.S. degree in geology . Hess then spent two years in northern Rhodesia (now Zambia) as an exploration geologist. Returning to the United States, Hess received his doctorate from Princeton University in 1932. He taught at Rutgers University for a year, conducted research at the Geophysical Laboratory at the Carnegie Institute of Washington, and then returned to Princeton in 1934. Hess would remain at Princeton for essentially the rest of his career, serving as chair of the university's geology department from 1950 to 1966.

Annette Burns, daughter of a botany professor at the University of Vermont, became Hess's wife in 1934. She was a source of strong support for Hess throughout his life, and accompanied him to conferences and scientific meetings. The couple had two sons.

As a professor at Princeton, Hess continued his work on mountain ranges and island arcs , which are arc-shaped chains of islands that usually contain active volcanoes. By 1937, he had developed a unifying hypothesis that tied together the creation of island arcs with the presence of gravity anomalies and magnetic belts of serpentine (a rock which is formed by the crystallization of magma ).

Hess's geological research was halted during World War II because he was a reserve officer in the Navy. He was initially assigned to duty in New York City, where he was responsible for estimating the positions of enemy submarines in the North Atlantic. Hess was then assigned to active sea duty and eventually became commander of an attack transport ship. This vessel carried equipment for sounding the ocean floor, and Hess took full advantage of it. He mapped a large part of the Pacific Ocean, discovering in the process the underwater flat-topped seamounts that he named guyots , in honor of A.H. Guyot, the first professor of geology at Princeton. The origin of guyots was puzzling, for they were flat on top as if they had been eroded off at the ocean surface, yet were two kilometers below sea level. As commander of the USS Cape Johnson, Hess also participated in four major combat landings, including one at Iwo Jima. Remaining a reserve officer after the war, Hess was called on for advice in such emergencies as the Cuban missile crisis in October 1962. By the time of his death he had achieved the rank of rear admiral.

After the war ended, Hess continued to study guyots as well as midocean ridges, which run down the centers of the Atlantic and Pacific Oceans like an underwater backbone. He also continued his mineralogical studies on the family of pyroxenes, an important group of rock-forming minerals . In 1955, he proposed that the boundary between the crust and the mantle of the earth is due to a change in the chemical composition of rocks.

During the 1950s, Hess became an influential backer of the ill-fated "Project Mohole," which proposed to drill a hole through the shallow oceanic crust into the earth's mantle for scientific sampling. In 1961, an experimental hole was bored through 11,600 ft (3,535 m) of water , 600 ft (183 m) of sediments, and 44 ft (13 m) of basalt . President John F. Kennedy telegraphed his congratulations to the National Science Foundation; John Steinbeck wrote an article for Life magazine about it. Despite amassing 25 million dollars in federal funding, Project Mohole foundered in 1966 under rising costs and political intrigue. It did, however, become an important stepping stone for the Deep Sea Drilling Project, successfully begun in the late 1960s.

Hess accepted visiting professorships at South Africa's Capetown University from 1949 to 1950, and at Cambridge University in 1965. Otherwise, he remained at Princeton until his death. He received numerous awards and honors, both at home and abroad, and was a major figure in the American Miscellaneous Society, a loosely-gathered group of scientists from different fields who liked to discuss "miscellaneous" ideas, such as Project Mohole.

From 1962 until his death, Hess chaired the Space Science Board that advised NASA on its lunar exploration program. He lived long enough to see the first person walk on the Moon in July 1969. One month later, while attending a space science conference in Woods Hole, Massachusetts, Hess died even as he was consulting a doctor about chest pains that he was experiencing.

Hess made a major contribution to the continental drift theory, which viewed continental and oceanic positions as the result of the break up of a single "supercontinent" (a theory first proposed by Alfred Wegener in 1912). Suggesting a mechanism by which continents could move away from each other without tearing up a rigid seafloor, Hess managed to unite several disparate elements: the youth of the ocean floor, the origin of midocean ridges, and the presence of island arcs and deep sea trenches surrounding the Pacific.

Hess's hypothesis gave geologists their first clue that drifting continents are carried passively on the spreading seafloor. In 1963, Fred Vine and Drummond Matthews at Cambridge University proposed a corollary to Hess's hypothesis: if the seafloor is created at the midocean ridges and spreads outward—and if the earth's magnetic field reverses polarity every few thousands of years—then the seafloor should be made of magnetized strips running parallel to the midocean ridges, alternating between normal and reverse polarity. Their idea, proposed independently by Lawrence Morley of the Geological Survey of Canada, was confirmed a few years later when scientists found the underwater bands of differently-magnetized rocks.

This oceanographic data established that continental drift does in fact occur. Over the next couple of years, geologists eventually accepted the new and revolutionary idea. Although certain details of Hess's seafloor spreading hypothesis have become outdated, its central idea—that seafloor is created at ridges and destroyed under continents—has become an important foundation of modern earth science .