Dietz, Robert Sinclair
Born Westfield, New Jersey, USA, 14 September 1914
Died Tempe, Arizona, USA, 19 May 1995
Robert Sinclair Dietz was a marine geologist, geophysicist, oceanographer, and professor of geology at Arizona State University. He is considered to have been one of the most influential geologists of the twentieth century. Dietz was the son of civil engineer Louis Dietz and his wife Bertha Dietz. In 1941, Robert completed his studies in geology and chemistry at the University of Illinois. He received all three of his degrees – B.S. (1937), M.S. (1939), and Ph.D. (1941) – from that institution.
Dietz served as a pilot in the United States Army Air Force during World War II and achieved the rank of lieutenant colonel. After the war, Dietz became a civilian scientist with the United States Navy at the Navy Electronics Laboratory [NEL] in San Diego, from 1946 to 1954 and from 1959 to 1963. He supervised the oceanographic research done in 1946–1947 on the last Antarctic expedition by Admiral Richard E. Byrd. From 1963 to 1970, Dietz was an oceanographer for the United States Coast and Geodetic Survey, and from 1970 to 1977 for its successor, the National Oceanographic and Atmospheric Administration.
During these years, Dietz undertook various expeditions to make soundings of the ocean’s depths and gathered core samples from the sea floor. Determinations of the geological ages of these igneous rocks led to his recognition of their increasing ages as measured away from the mid-ocean rift zones and Dietz’s proposal of the notion of “sea floor spreading.” These findings, which he published in Naturein 1961, became one of the cornerstones of the modern theory of plate tectonics.
On leave from the NEL, Dietz spent 1953 on a Fulbright Fellowship in Japan and from 1954 to 1958 working in London with the Office of Naval Research. At a deep-sea diving symposium in 1955 in London, he met Swiss oceanic engineer, economist, and physicist Jacques-Ernest-Jean Piccard, builder of the bathyscaph Trieste. On 23 January 1960, Piccard and Lieutenant Don Walsh of the United States Navy set a new submarine depth record by descending 10,911 m (35,798 ft) into the Mariana Trench in the Pacific Ocean. Piccard selected Dietz to coauthor the documentary account of those deep-sea dives. In 1961, their book, Seven Miles Down: Story of the BathyscaphTrieste, was published.
During and shortly after World War II, Dietz also investigated the process of crater formation on the surface of the Moon. The real turn in the scientific acceptance of the lunar crater impact theory came in the 1940s with the publication of two key papers and a monograph by American astronomer Ralph Baldwin . Dietz likewise advocated the impact theory in a 1946 paper published in the Journal of Geology. In these articles, Baldwin and Dietz persuasively demonstrated that the vast majority of the Moon’s craters were of impact origin.
Concurrently, Dietz (1947) proposed an impact origin for the geological disturbance found at Kentland, Indiana, from the evidence of shatter cones. This became the first of more than 130 structures that Dietz and his colleagues gradually identified as having an impact origin. The most significant of these was his recognition in 1964 of the 40-mile diameter depression at Sudbury, Canada, which resulted from the impact of a nickel-iron meteorite some two billion years ago. In 1960, Dietz had coined the term “astrobleme” for terrestrial structures that are considered to have been of impact origin. The term comes from the Greek roots “astro,” meaning “star,” and “bleme,” meaning “a wound caused by a thrown object.” In 1973, Dietz completed a study of the semicircular structure of Hudson’s Bay in Canada. But from the absence of shatter cones or “suevite-type or other unusual melt rocks . . . and other possible shock metamorphic effects,” he concluded that it was not the result of a gigantic meteorite impact, as had been suggested.
In 1963, while Dietz was employed by the United States Coast and Geodetic Survey, he participated in an expedition to map the floor of the Ganges River delta’s submarine canyon in the Indian Ocean. Dietz also participated in oceanographic expeditions along the coast of West Africa, including studies of submarine trenches off the coasts of Portuguese Guinea and Mauritania. But after federal budgets for oceanographic research were deeply cut in the 1970s, Dietz left government employment and took temporary teaching positions at the University of Illinois, Washington University (Saint Louis), and Washington State University, before landing a fulltime position as professor of geology at Arizona State University in 1977. Although retiring in 1985, Dietz remained an active emeritus professor until his death.
During his career, Dietz received the Penrose Medal, the highest award of the Geological Society of America, along with the Barringer Medal of the Meteoritical Society for his pioneering work on crater formation. The American Geophysical Union likewise honored Dietz by awarding him the Walter H. Bucher Medal for his original contributions to the study of plate tectonics. Asteroid (4666) Dietz has been named after him.
- — (1947). “Meteorite impact suggested by the orientation of shatter-cones at the Kentland, Indiana disturbance.” Science105: 42–43.Google Scholar
- — (1961). “Continent and ocean basin evolution by spreading of the sea floor.” Nature190: 854–857.Google Scholar
- — (1994). “Earth, Sea, and Sky: Life and Times of a Journeyman Geologist.” Annual Review of Earth and Planetary Sciences22 (May 1994): 1–32.Google Scholar
- — (1999). “Memorial to Robert Sinclair Dietz, 1914–1995.” Geological Society of America Memoirs29: 25–27.Google Scholar