(b. Ypsilanti, Michigan, 30 July 1920;
d. Nyack, New York, 23 August 2006), cartography, sea-floor mapping, oceanography.
One of the most influential cartographers of the mid-twentieth century, Tharp created the first physiographic maps of the seafloor. These maps, made in collaboration with the geologist Bruce Heezen, were the first to reveal the detailed topography and multi-dimensional geographical landscape of the ocean bottom; they became significant evidence for the emerging theory of plate tectonics in the late 1960s. A research associate at Columbia University’s Lamont Geological Observatory for the first part of the career, Tharp worked as an independent researcher after the late 1960s.
Early Years. Marie Tharp was born in Ypsilanti, Michigan, the daughter of William Edgar Tharp, a soil surveyor for the federal Bureau of Chemistry and Soils, and Bertha Louise (Newton) Tharp, a teacher of German and Latin. Her father’s work caused the family to move frequently, and Tharp attended more than twenty different public schools in six states and the District of Columbia. After her father’s retirement in 1931, the family settled on a farm in Bell Fountain, Ohio, where Tharp graduated from high school. She subsequently enrolled in the University of Ohio.
Tharp had not decided on a major when she started college. Her father insisted that she pick a subject that she liked and that would offer her a way to earn her own living. While at Ohio, Tharp changed her major every semester, and might have decided to become a teacher had her mother not died before she graduated. She received her bachelor’s degree in English and music in 1943.
While she was finishing her degree at Ohio, Tharp happened upon a brochure from the University of Michigan’s geology program encouraging young women to apply for graduate training to prepare for positions in the petroleum industry. With classrooms empty of men during the war years, Michigan—which had never allowed women into its geology program—was trying to fill seats. Tharp jumped at the chance, graduated with a master’s degree in 1944, and went to work for Standlind Oil and Gas Company in Tulsa, Oklahoma, as a junior geologist. Upon her arrival, she discovered that women were not allowed to do field work, and so Tharp was stuck in an office coordinating maps and data for her male colleagues. During this time, she took enough courses at the University of Tulsa to earn a second bachelor’s degree in mathematics in 1948.
East to Columbia University. Four years in Tulsa left Tharp eager for a new challenge that would include research. She headed east to Columbia University and found a position as a research assistant to geology graduate student Bruce Heezen. Heezen worked under the direction of the eminent geophysicist W. Maurice Ewing. He became her close professional collaborator and the two worked together as a creative couple, a relationship that continued almost thirty years until Heezen’s death in 1977.
Her initial task at Columbia involved compiling oceanic bathymetry data. Prior to World War II, only widely scattered measurements had been made in the deep oceans, principally by government-sponsored expeditions such as those conducted by the British HMS Challenger(1872–1876) and the German Meteor (1925–1927). Although these expeditions had revealed certain large-scale features, including an extended rise called the Mid-Atlantic Ridge, the general characteristics of the seafloor remained largely unknown.
Interest in the oceans increased during and after World War II, owing to military concerns with understanding the ocean environment for anti-submarine warfare. By the early 1950s Heezen (now a junior PhD associate of Ewing at Columbia’s new Lamont Geological Observatory) and his colleagues began gathering wide-ranging data on the ocean floor, including its elevation. Tharp’s role at Lamont expanded to include assessing the reliability of past and contemporary depth measurements and interpreting the geographic landscapes they began to reveal. In the process Tharp made one of her most important discoveries: a rift valley bisecting the Mid-Atlantic Ridge that was structurally similar to the Great Rift Valley in Africa. Initially Heezen refused to accept this find, but relented after noticing that seismological records of undersea earthquake epicenters correlated with the mid-Atlantic rift valley. As precise measurements extended across Earth’s oceans, Heezen, Tharp, and Ewing also discovered that the Mid-Atlantic Ridge was part of a 40,000 mile long world-encircling ridge system, the largest tectonic feature on Earth’s surface and a significant geological finding.
Seafloor Cartography. In 1952 Heezen sought to make a detailed map of the North Atlantic seafloor, aware that existing maps were coarse and provided limited insight into distinct geographical provinces and landforms (including abyssal plains and mountain ridges) that depth soundings were revealing. He and Tharp decided against making a contour map in favor of a physiographic one, portraying physical features from an oblique perspective with scale and position carefully controlled. They did this for several reasons: beyond providing a realistic bird’s eye view, a physiographic map enabled them to circumvent navy classification policies because it did not provide precise depth data. By 1957, with support from telecommunications companies then laying the first transatlantic undersea telephone lines, Heezen and Tharp completed their pioneering detailed physiographic map of the North Atlantic Ocean seafloor, one of the most significant new maps of the twentieth century.
In the 1960s and 1970s Heezen and Tharp extended their mapping project to all the world’s oceans. Drawing on her artistic and drafting skills to create individual ocean basin maps, Tharp worked with Heezen and also the Austrian artist Heinrich Berann to produce the 1977 “World Ocean Floor” panorama, a widely circulated iconic map that depicted what was then known about seafloor topography. While these maps stimulated geophysical and oceanographic research—Heezen used the North Atlantic map to support the expanding Earth concept—the mapping project also exacerbated tensions between Heezen and Ewing involving publication credit and priority. In the late 1960s Ewing barred Tharp, who unlike Heezen did not occupy a tenured position, from working at Lamont, causing her to shift her mapping work to her nearby home.
Awards and Later Career. Tharp gained her first opportunity to go to sea in 1965 on a research cruise Heezen organized on Duke University’s R/V Eastward (at Lamont, Ewing still prohibited women from working at sea).
Largely invisible as a researcher early in her career, Tharp gained recognition for her geographic insights and cartographic skills later in life. She received awards from the Geography and Map Division of the Library of Congress and Woods Hole Oceanographic Institution, as well as the first annual Lamont-Doherty Earth Observatory Heritage Award in 2001. Four years later, Lamont created the Marie Tharp Visiting Fellowship program to aid promising women researchers.
After Heezen’s death, Tharp remained a professional map-maker, selling copies of the Heezen-Tharp seafloor maps from her research office-home in Nyack, New York, overlooking the Hudson River. Largely unfazed by the intense professional rivalry between Heezen and Ewing, Tharp was regarded by Lamont colleagues as intensely focused, wholly devoted to Heezen, and largely unconcerned with fashion or worldly pursuits. Tharp died of cancer in Nyack, New York, in August 2006.
A collection of transcribed oral history interviews with Tharp resides at the Niels Bohr Library of the American Institute of Physics in College Park, Maryland. Her map collection is held at the Geography and Map Division of the U.S. Library of Congress.
WORKS BY THARP
With Bruce C. Heezen. “Physiographic Diagram of the North Atlantic.” Geological Society of America Bulletin 67 (1956): 1704.
With Bruce C. Heezen and Maurice Ewing. The Floors of the Ocean. Geological Society of America Special Paper 65. New York: Geological Society of America, 1959.
With Bruce C. Heezen. “Tectonic Fabric of the Atlantic and Indian Oceans and Continental Drift.” Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences 258, no. 1088 (1965): 90–106.
With Henry Frankel. “Mappers of the Deep: How Two Geologists Plotted the Mid-Atlantic Ridge and Made a Discovery that Revolutionized the Earth Sciences.” Natural History 95, no. 10 (1986): 49–62.
Barton, Cathy. “Marie Tharp, Oceanographic Cartographer, and Her Contributions to the Revolution in the Earth Sciences.” In The Earth Inside and Out: Some Major Contributions to Geology in the Twentieth Century, edited by David R. Oldroyd. London: Geological Society, 2002.
Doel, Ronald E., Tanya J. Levin, and Mason K. Marker. “Extending Modern Cartography to the Ocean Depths; Military Patronage, Cold War Priorities, and the HeezenTharp Mapping Project, 1952–1959.” Journal of Historical Geography 32 (2006): 605–626.
Ronald E. Doel
Kristine C. Harper
Geologist Marie Tharp (born 1920) is known for her maps of ocean floors. These maps are helpful in showing the structure and evolution of the sea floors.
Marie Tharp is a mapmaker who charted the bottom of the ocean at a time when little was known about undersea geology. Her detailed maps showed features that helped other scientists understand the structure and evolution of the sea floor. In particular, Tharp's discovery of the valley that divides the Mid-Atlantic Ridge convinced other geologists that sea floor was being created at these ridges and spreading outward. The confirmation of "seafloor spreading" led to the eventual acceptance of the theory of continental drift, now called plate tectonics.
Tharp was born in Ypsilanti, Michigan, on July 30, 1920. Her father, William Edgar Tharp, was a soil surveyor for the United States Department of Agriculture's Bureau of Chemistry and Soils; he told his daughter to choose a job simply because she liked doing it. Marie's mother, Bertha Louise (Newton) Tharp, taught German and Latin. The family moved frequently because of William Tharp's mapping assignments across the country. Marie Tharp attended twenty-four different public schools in Iowa, Michigan, Indiana, Alabama (where she almost flunked out of the 5th grade in Selma), Washington, D.C., New York, and Ohio. In 1943 she received her bachelor's degree from Ohio University.
Since most young men were fighting in World War II at the time Tharp graduated, the University of Michigan opened the doors of its geology department to women for the first time. Tharp entered the masters program, which trained students in basic geology and then guaranteed them a job in the petroleum industry. Graduating in 1944, Tharp was hired as a junior geologist with Stanolind Oil & Gas in Tulsa, Oklahoma. Women were not permitted to search for oil in the field, so Tharp found herself organizing the maps and data for the all-male crews. While working for Stanolind, Tharp earned a B.S. in mathematics from the University of Tulsa in 1948.
The year of her second bachelor's degree, Tharp moved to Columbia University, where a group of scientists were about to revolutionize the study of oceanography. Hired as a research assistant by geologist Maurice Ewing, Tharp actually ended up helping graduate students with their data; she never told anyone that she had a graduate degree in geology. One student, Bruce Heezen, asked for help with his ocean profiles so often that after a while Tharp worked with him exclusively. Heezen and Tharp were to work closely together until his death in 1977. In 1950 the geophysical laboratory moved from Columbia University to the Lamont Geological Observatory in Palisades, New York.
Before the early 1950s, scientists knew very little about the structure of the ocean floor. It was much easier and cheaper to study geology on land. But without knowledge of the structure and evolution of the seafloor, scientists could not form a complete idea of how the entire earth worked. In the 1940s, most people believed that the earth was a shrinking globe, cooling and contracting from its initial hot birth. The work of Heezen, Tharp, and other geologists in the next decade—who gathered data on the sea floor using echo sounding equipment—helped replace that idea with the model of plate tectonics, where thin crustal "plates" shift around on the earth's mantle, colliding and grinding into each other to push up mountains and cause earthquakes.
The Mid-Atlantic Ridge, a mountainous bump that runs roughly parallel to and between the coastlines of the Americas and Africa, was one of the first topographical features on the sea floor to be identified. Initial studies were undertaken by those aboard the British ship H.M.S. Challenger, who discovered in the 1870s that the rise in the center of the Atlantic acted as a barrier between different water temperatures; and by those aboard the German ship Meteor who between 1925 and 1927 revealed the Mid-Atlantic Ridge as rugged and mountainous. The Meteor staff also found several "holes" in the center of the Ridge, but did not connect these holes into the continuous rift valley that they were later discovered to be. In the 1930s, the British geologists Seymour Sewell and John Wiseman suspected that a rift valley split the Ridge, but World War II prevented an expedition to confirm this.
By 1950, when Tharp and Heezen moved to Lamont, the time was right for a series of discoveries. In 1952, the pair decided to make a map of the North Atlantic floor that would show how it would look if all the water were drained away. This type of "physiographic" diagram looked very different from the usual method of drawing contour lines for ocean floor of equal depth. Heezen and Tharp chose the physiographic method because it was a more realistic, three-dimensional picture of the ocean floor, and also because contours were classified by the U.S. Navy from 1952 to 1962.
Tharp assembled her first drawing of the North Atlantic ocean floor in 1952, after rearranging Heezen's data into six seafloor profiles that spanned the Atlantic. This initial map showed a deep valley dividing the crest of the Mid-Atlantic Ridge. Tharp pointed out the valley to Heezen. "He groaned and said, 'It cannot be. It looks too much like continental drift, "' Tharp wrote later in Natural History. The valley represented the place where newly-formed rocks came up from inside the earth, splitting apart the mid-ocean ridge. At the time, Heezen, like most scientists, thought that continental drift was impossible.
While Tharp was working on detailing and clarifying the first map, Heezen kept another assistant busy plotting the location of the epicenters of North Atlantic earthquakes. Beno Gutenberg and Charles F. Richter had already pointed out that earthquake epicenters followed the Mid-Atlantic Ridge quite closely. But Heezen's group found that the epicenters actually fell within the suspected rift valley. The association of topography with seismicity convinced Tharp that the valley was indeed real.
It took Heezen eight months to agree. By studying rift valleys in eastern Africa, Heezen convinced himself that the land in Africa was simply a terrestrial analogy to what was going on in the middle of the Atlantic: the earth's crust was splitting apart in a huge tensional crack. Heezen then began to wonder whether the earthquake epicenters that had been recorded in the centers of other oceans might also lie in rift valleys. Perhaps, he thought, all the mid-ocean ridges could be connected into a huge 40, 000 mile system.
Heezen told Maurice Ewing, director of Lamont, of the valley's discovery. For several years, only Lamont scientists knew of its existence. Heezen presented it to the scientific community in several talks during 1956. In 1959, most of the remaining skeptics were convinced by an underwater movie of the valley, made by French oceanographer Jacques Cousteau towing a camera across it. Today scientists understand how the rift valley represents the pulling apart of the seafloor as the new rock spreads outward from the ridge.
Heezen and Tharp printed their first edition of the North Atlantic map for a second time in 1959. By this time they knew that the Mid-Atlantic Ridge was cut by east-west breaks, now called transform faults. Heezen and Tharp had confirmed only one of these breaks, but they didn't know its exact length or direction. So in its place on the map they put a large legend to cover the space. In the following years, Tharp and Heezen improved their North Atlantic map and expanded their work to cover the globe, including the South Atlantic, Indian, Arctic, Antarctic, and Pacific oceans. In 1977, three weeks before Heezen's death, they published the World Ocean Floor Panorama, based on all available geological and geophysical data, as well as more than five million miles of ocean-floor soundings. In 1978 Tharp and Heezen received the Hubbard Medal of the National Geographic Society.
After about fifteen years of work behind the scenes, Tharp finally went on research cruises herself, including trips to Africa, the Caribbean, Hawaii, Japan, New Zealand, and Australia. She retired from Lamont in 1983. Since then she has run a map distributing business in South Nyack, New York, and occasionally consults for various oceanographers. She also keeps Heezen's scientific papers and has written several articles on his life and work. Tharp enjoys gardening in her spare time.
Oceanus, winter, 1973-74, pp. 44-48. □