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Marie Tharp’s innovative maps brought the seabed to the world

Walk through the corridors of an academic department of earth sciences and you’ll likely find on a wall somewhere a beautiful map of the world’s ocean floor. Completed in 1977, the map represents the culmination of Marie Tharp’s unlikely and underrated career. Her three decades of work as a geologist and cartographer at Columbia University have given scientists and the public a first look at the appearance of the seabed.

In the mid-20th century, when many American scientists rebelled against continental drift, the controversial idea that continents are not fixed in place, Tharp’s innovative maps helped tilt the scientific view toward acceptance and clear the way for the emerging theory of plate tectonics.

Tharp was the right person in the right place at the right time to make the first detailed maps of the seabed. Specifically, she was the right woman. Their gender meant that certain career paths were essentially out of bounds. But she was able to take advantage of open doors due to historical circumstances, becoming the only one qualified to make significant contributions to both science and cartography. Without it, it’s possible the maps never would have been.

"It was a unique opportunity for life, once in the history of the world, for anyone, but especially for a woman in the 1940s," Tharp recalled in a 1999 perspective. "The nature of the times, the state of science, and the great events and small, logical and illogical, combined to make everything happen. "

With funding from the United States Navy, Marie Tharp and Bruce Heezen drew up this 1977 map with Austrian painter Heinrich Berann. He became iconic among cartographers and earth scientists.Library of Congress, Division of Geography and Map

Tharp’s cartographic roots have deepened. She was born in Michigan in 1920 and as a young girl would accompany her father on field trips to inspect lands and make maps for the U.S. Department of Agriculture’s Bureau of Soils, a job that kept the family moving. “When I finished high school I had attended almost two dozen schools and seen many different landscapes,” Tharp recalled. "I guess I had maps in my blood, even though I hadn't thought to follow in my father's footsteps."

Tharp was a student at Ohio University in 1941 when the attack on Pearl Harbor emptied campuses of youths joining the military en masse. This sudden shortage of male students caused the University of Michigan’s geology department to open its doors to women. Tharp had taken a couple of geology classes and jumped at the chance. “There were 10 or 12 of us from all over the United States, girls. With a sense of adventure, "he recalled in an oral history interview in 1994. Tharp earned a master's degree in 1943, completing a summer course on geological mapping and working as a part-time draftsman for the U.S. Geological Survey along the way. graduating, he took a job with an oil company in Oklahoma, but was bored with a job that involved neither fieldwork nor research.So he enrolled in evening classes to get a second master’s degree in math from the University of Tulsa.

Looking for more excitement, she moved to New York in 1948. When she entered the geology department at Columbia University looking for a job, her advanced degrees got her an interview, but the only position available to a woman was as a draftsman helping graduate students. working towards a degree in geology that he had already obtained. Still, he looked more promising than the other work he had asked about – studying fossils at the American Museum of Natural History – so he took it.

The following year Tharp became one of the first women employed at the newly founded Lamont Geological Observatory in Columbia and soon worked exclusively with geologist Bruce Heezen, a newly minted doctorate. Like many of Lamont's male scientists, Heezen was primarily concerned with collecting data about the ocean, which Tharp would then analyze, trace, and trace a map he was more than qualified to make.

“These men found it glamorous and enjoyable to go to sea, much more than stay home to analyze (the data),” writes Harvard University science historian Naomi Oreskes in her upcoming book Science on a Mission: How Military Funding Shaped What We do and we don’t know about the ocean. "This is one of the reasons why women have stopped data analysis." In fact, women were often not allowed on research vessels.

black and white data chartsTo generate the seabed maps, Marie Tharp started with two-dimensional ocean profiles (above) and then used her extensive geological knowledge to decipher the shapes of the terrain and fill in the blanks (below).A.C. Heezen, M. Tharp, and M. Ewing / Lamont-Doherty Earth Observatory / Special Society 1965 Geological Society of America

Aside from ocean expeditions, Tharp put all his energy into mapping the seabed starting in the North Atlantic, work that would lead to two important discoveries. To make a map, he first translated the echo depths collected by ships crossing the ocean to depths and then created vertical strips of terrain in two dimensions under the ships ’tracks. These profiles at the bottom of the ocean showed a wide ridge running across the middle of the Atlantic. Although the feature had been mapped around the 19th century, Tharp noticed a notch near the top of the ridge in each of the profiles. She believed the notches represented a continuous, deep valley that ran through the center of the mid-ocean ridge. If he was right, the valley could be a fissure where the molten material emerged from below, forming a new crust and separating the ocean floor, evidence that could support continental drift.

The idea that the continents were not fixed in place gained strength in Europe, but Heezen, like most American scientists of the time, "considered it almost a form of scientific heresy," Tharp later wrote in the journal Natural History. . It took a year or so to convince Heezen that the rift was real, and it took two more years to complete his first map of the North Atlantic in 1957.

To publish that first map and share their work with other scientists, Tharp and Heezen had to avoid the U.S. Navy’s Cold War-inspired decision to classify detailed topographic maps that used level lines to indicate depths. This was one of the reasons the couple chose to adapt a relatively new cartographic style known as a physiographic diagram, a kind of three-dimensional sketch of the terrain as if viewed from an airplane window. To do so, Tharp had to use his training as a geologist and his experience with cartography on land: knowledge and skills that a typical research assistant or draftsman would not have.

Physiographic maps had already been used to represent continental landforms with standardized symbols. Each type of mountain, valley, plain, and desert was sketched in a specific way. Tharp and Heezen were the first to use the technique to show how it could be an unknown and invisible terrain. Tharp first sketched a strip of seabed along each profile, deciphering what kind of clock each bump and dive was likely to be. He then identified patterns to fill in the blanks between the profiles.

detailed map of clocksThe physiographic maps of Bruce Heezen and Marie Tharp, this one of the North Atlantic published for the first time in 1957 and again in 1959, gave to the scientists a convincing visual comparison with the continental forms of relief that understood.Physiographic diagram of the North Atlantic Ocean (1959) by Heezen and Tharp; reproduced with permission from Marie Tharp Maps LLC and the Lamont-Doherty Earth Observatory

“The amount of work involved just taking it out of those polls and being able to create that is incredible,” says historian Judith Tyner, author of Women in American Cartography.

When Tharp was creating his map, an unrelated project was taking shape on the writing desk next to his. Heezen had hired a recent graduate of an art school to trace thousands of earthquake epicenters in the Atlantic Ocean to help Bell Laboratories find the safest places to lay transoceanic cables. The epicenters he traced lined up with the valley of the Tharp rift. The correlation gave weight to the idea that the slit was where the crust separated and gave Tharp a way to accurately locate the slit between the ship’s tracks.

The Heezen and Tharp diagram of the 1957 Atlantic Ocean was by far the most comprehensive seabed map ever produced.

“The marvel of that map is the vastness that had fairly limited data,” says science historian Ronald Doel of Florida State University in Tallahassee. "But the earthquake data also helped make it clear where the ridges are oriented and where the associated geological features are."

The American scientific community was initially skeptical, distrustful of the speculative nature of its map. But as the pair continued to map the rest of the Atlantic and advance into other oceans, evidence accumulated over a continuous ridge, with a rift valley at its center, stretching for about 60,000 miles worldwide.

Tharp and Heezen’s innovative use of the physiographic method gave scientists a compelling visual comparison with the continental landforms they understood. This helped convince them that just as the East African Rift was dividing that continent, the submarine Rift Valley marked where the continents on both sides of the Atlantic had receded.

“That’s why its map is so powerful,” says geology historian David Spanagel of the Worcester Polytechnic Institute in Worcester, Massachusetts. "It allows people to see the bottom of the ocean as if it were a piece of land and then reason with it. That's something transformative that she's capable of accomplishing."

National Geographic also learned about the maps and invited Heezen and Tharp to collaborate on some ocean illustrations with Austrian painter Heinrich Berann, who would become famous for his mountain panoramas. Magnificent representations of the ocean floor were included as poster-size supplements in issues of National Geographic magazine between 1967 and 1971. The magazine had a circulation of 6 or 7 million at the time, giving a large audience a window into the ocean.

In 1973, Heezen and Tharp received a grant from the US Navy to work with Berann on a complete map of the world's ocean floor. It took the trio four years to create their iconic cartographic masterpiece, an unparalleled panoramic view that continues to shape how scientists and audiences think on the seabed.

The map ended a few weeks before Heezen died of a heart attack at age 53, while on a submarine exploring the ocean ridge near Iceland. His death left Tharp without a source of funding and data, and essentially ended his remarkable career. It would be decades before his contributions were fully recognized. But unlike many other unsung figures in the history of science, the awards began to take place before he died of cancer in 2006. During the last decade of his life, Tharp received prestigious awards from several institutions, including Lamont, now known as Lamont-Doherty. Earth Observatory and Library of Congress, which named her one of the four best cartographers of the 20th century.

"Can you imagine how high he would have risen in his profession," says Tyner, "if he had been a man?"

Although his was always the second name, after Heezen, in the maps they made, and does not appear at all in the papers to which his work contributed, Tharp never expressed any remorse for his path. “I thought I was lucky to have such an interesting job,” he recalled in 1999. “Set up the rift valley and the mid-ocean ridge that ran all over the world for 40,000 miles – that was something important … You don’t find anything else bigger than that, at least on this planet. "

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