Harry Hammond Hess

Geologist

• Born: May 24, 1906
• Birthplace: New York, New York
• Died: August 25, 1969
• Place of death: Woods Hole, Massachusetts

American geologist

American geologist Harry Hammond Hess developed the theory of seafloor spreading. This helped scientists come to a consensus about plate tectonic theory and changed the way people understood the formation of the Earth.

Born: May 24, 1906; New York, New York

Died: August 25, 1969; Woods Hole, Massachusetts

Primary field: Earth sciences

Specialties: Geology; geophysics; oceanography

Early Life

Harry Hammond Hess was born in New York City on May 24, 1906. In 1923, he enrolled at Yale University in New Haven, Connecticut. He intended to pursue a degree in electrical engineering, but his interests shifted to geology. Hess earned his bachelor’s degree in 1927 and moved to Rhodesia (now Zimbabwe), where he worked as a mineral prospector for two years. Upon returning, Hess enrolled in graduate courses at Princeton University in New Jersey, where he studied under petrologist Arthur Buddington.

Petrology is the study of the formation and composition of rocks. Much of Hess’s research at Princeton concerned the structure of peridotite, a dense igneous rock that contains the element olivine. Peridotite, of which the Earth’s mantle is primarily composed, was the focus of Hess’s doctoral thesis. In addition to his thesis, Hess wrote several papers that became influential geological documents. While working toward his doctoral degree, Hess traveled to the Caribbean to conduct underwater study. His mentor on the excursion was the renowned Dutch geophysicist F. A. Vening Meinesz. Using naval submarines as laboratories, Hess and Meinesz conducted experiments in the region of the Lesser Antilles islands.

Upon finishing his PhD at Princeton in 1932, Hess taught at Rutgers University in Newark, New Jersey, and worked as a research associate at the Geophysical Laboratory of the Carnegie Institution of Washington, DC. Hess began teaching at Princeton in 1934 and earned tenure as a professor of geology in 1950.

Life’s Work

During his years on the Princeton faculty, Hess also taught as a visiting professor at the University of Cape Town in South Africa from 1949 to 1950 and at the University of Cambridge in England in 1965. He was elected to a number of institutions, including the National Academy of Sciences (1952), the American Philosophical Society (1960), and the American Academy of Arts and Sciences (1968). Additionally, Hess was elected president of the Mineralogy Society of America (1955), the Geological Society of America (1963), and the Geodesy and Tectonophysics branches of the American Geophysical Union (1951 and 1956). In 1950, Hess became chair of the geology department at Princeton, a position he held until 1966. He succeeded Buddington as Blair Professor, a distinction awarded to outstanding professors, in 1964.

Although Hess had already conducted research with peridotite and had published several noteworthy papers, his career breakthrough came during a period of service in the United States Navy. Hess enlisted in the Navy Reserve and was called upon in 1941 to assist in the detection of German U-boats in the northeast Atlantic. Afterward, he requested a transfer to the USS Big Horn, which was built as a decoy to help determine whether the navy’s detection systems were effective. Hess served on the Big Horn during the early part of the war. He was then appointed captain of the USS Cape Johnson, a large transport vessel assigned to tour the South Pacific.

During the tour, Hess used the ship’s sonar technology, a new echo-sounding device, to gather information about the ocean floor. With the data he collected, Hess was able to map strategic routes to the South Pacific. In the process of surveying thousands of miles of the ocean floor, Hess noticed its distinct geological features. Hess detected the presence of raised, flat-topped platforms at the bottom of the ocean. He hypothesized that the platforms were the remnants of islands that sank thousands of years earlier. Hess named the platforms “guyots,” in honor of Swiss geographer Arnold Guyot, the founder of the geology department at Princeton.

From his recorded observations, Hess formulated the theory of seafloor spreading to explain the features and arrangement of the rocks that make up the ocean floor. British geologist Arthur Holmes had conducted similar research in the 1930s. Hess’s theory included both Holmes’s original ideas and conclusions based on his own observations. Hess outlined the theory of seafloor spreading in a paper in 1960. Because he had very little concrete evidence or time-lapse observations of the ocean’s floor, he did not publish the paper in a scholarly journal, and thus the theory received little recognition. However, Hess decided to expand his work despite the lack of initial support.

In 1962, Hess published “History of Ocean Basins.” The paper discusses the theory of plate tectonics—the movement of continental plates—with regard to Hess’s theory of seafloor spreading. Hess theorized that molten rock escapes the Earth’s core through ridges in the oceanic crust. The escaped rock pushes the seafloor apart as it cools, and falls into deep trenches. Hess maintained that although the oceans had existed for four billion years, the sediment and other rock formations presently on the ocean floor had only been around for 300 million years. He also suggested that seafloor spreading is primarily caused by mantle convection cells, heating and cooling currents that cause the Earth’s mantle to move. “History of Ocean Basins,” later considered a seminal work in plate tectonics, resulted in the widespread acceptance of the theory of seafloor spreading. The paper answered a number of geological questions regarding the nature of the ocean floor.

In 1957, American oceanographer Walter Munk initiated a campaign to drill through the ocean’s floor and into the underlying mantle. This effort, called the Mohole Project, became a matter of intrigue and controversy for geologists and politicians. A proponent of the Mohole Project, Hess served as its scientific advisor. Drilling began near Guadalupe, Mexico, in 1958. The Mohole Project was successful in providing mantle samples and information about the Earth’s crust. Divided into three phases, the project continued for nearly a decade. However, due to the increasing expense of the project, the US Congress suspended the Mohole Project indefinitely in 1966.

US President John F. Kennedy took note of Hess’s accomplishments and appointed him chairman of the Space Science Board of the National Academy of Sciences. In this position, Hess assisted in the design and development of the US space program.

In recognition of his theory of seafloor spreading, Hess received the Geological Society of America’s Penrose Medal in 1966, the geologists’ equivalent to the Nobel Prize. Yale University awarded Hess an honorary PhD in 1969. The Space Science Board later appointed Hess to chair a meeting at Woods Hole, Massachusetts. During the meeting, on August 25, 1969, Hess suffered a fatal heart attack.

Impact

As more scientists studied the ocean floor, they began to accept Hess’s theory of seafloor spreading as the mechanism behind continental drift. By 1967, seafloor spreading was the dominant theory in the field, and virtually all Earth scientists were reinterpreting their data in light of it. The idea of seafloor spreading led to an overall theory of plate tectonics, which was developed in the 1960s and soon became accepted as fact. The theory of plate tectonics explains the formation and distribution of the Earth’s continents, including details such as why earthquakes occur.

Hess’s theory of seafloor spreading had an impact on geology comparable to that of Darwin’s theory of evolution on the field of biology. Upon his death, the National Academy of Sciences wrote that Hess was one of the most significant Earth scientists of the twentieth century. The National Aeronautics and Space Administration (NASA) posthumously awarded Hess the Distinguished Public Service Award. Because Hess provided invaluable leadership, research, and funding to a range of scientific fields, the American Geophysical Union named an award of distinction in Hess’s honor in 1984. The Harry H. Hess Medal is awarded to people who demonstrate “outstanding achievement in research in the constitution and evolution of Earth and sister planets.”

Bibliography

Blatt, Henry, Robert Tracy, and Brent Owens. Petrology: Igneous, Sedimentary, and Metamorphic. 3rd ed. New York: Freeman, 2006. Print. Overview of the three basic rock groups of petrology, the area of geology in which Hess specialized.

Frankel, Henry R. The Continental Drift Controversy: Introduction of Seafloor Spreading. Vol. 3. New York: Cambridge UP, 2012. Print. Covers the introduction of, debate over, and acceptance of continental drift theory. This volume discusses marine geology and geophysics during the Cold War, with a chapter devoted to Hess.

Lawrence, David M. Upheaval from the Abyss: Ocean Floor Mapping and the Earth Science Revolution. Piscataway, NJ: Rutgers UP, 2002. Print. History of the theory of plate tectonics, including Hess’s work.

Oreskes, Naomi, ed. Plate Tectonics: An Insider’s History of the Modern Theory of the Earth. Cambridge, MA: Westview P, 2001. Print. Essays by scientists who helped develop the theory of plate tectonics, covering various aspects of the theory. Discusses Hess and includes a history of plate tectonics, key terms, and how scientists collaborated to understand the theory.