Marie Tharp: the Woman Who Mapped the Ocean Floor

By Jaime Seltzer

Marie Tharp was born in 1920 in Ypsilanti, Michigan, the city so unpronounceable even its inhabitants call it ‘Ypsi’. Her mother, Bertha, was a language teacher who instructed in Latin and German before she married her father, William, who was a soil scientist who made maps for the U.S. Department of Agriculture.

William Tharp’s work meant a great deal of travel to analyze local geological formations, and so the family moved as a group for every new project: by the time Marie was fifteen, she had moved thirty times. Without any siblings close to her in age, Marie had to find her own amusements, which were solitary in nature: she loved to read, and she’d go out on trips with her father to Do Science.

“At this point, Marie had a bachelor’s in English, mathematics, and music, four minors, and a master’s in geology, but due to her second X chromosome, she still only qualified to be a research assistant at Lamont Laboratory at Columbia University.”

Marie attended to Ohio University, where she double-majored in music and English and earned not one, not two, not three, but four minors in different subjects. In other words, she could have written this essay, translated it to French, set it to music and based an equation on its meter and rhyme.

The start of World War II changed Marie Tharp’s path as it did for so many women. Suddenly, recruiters were snatching up any young women who’d so much as taken a science course and strongly encouraging them to earn graduate degrees and work in the field. Tharp thought it sounded pretty cool to learn yet more new stuff, and so become a Petroleum Geology Girl, one of ten at the University of Michigan at Ann Arbor.

The first real job Marie obtained was essentially high-paid secretarial work, and Tharp was not impressed. Figuring that becoming the most educated woman in history might land her additional job opportunities, she went on to earn a degree in mathematics, this time. At this point, Marie had a bachelor’s in English, mathematics, and music, four minors, and a master’s in geology, but due to her second X chromosome, she still only qualified to be a research assistant at Lamont Laboratory at Columbia University.

Marie was really quite lucky to have landed a spot at Lamont. Despite being of a lady-type persuasion, she did slowly advance through the ranks, earning more privileges and a higher salary as she went. However, interesting projects and fieldwork still tended to go to men, and the tedious mathematical calculations and desk work went to the women. She was also untenured for a scandalously long time, which meant that she could be fired anytime someone took the fancy.

When the Lamont scientists started a project that involved mapping the ocean floor, women were not allowed on the ships due to Navy regulations. You heard me right: women could not go on ships. Some sources say that the lab director considered them ‘bad luck at sea’, which was actually a thing. Say it with me: you can’t make this stuff up.

Again, Tharp’s luck – or people skills – prevailed. She and a scientist named Bruce Heezen developed a you-scratch-my-back-I’ll-scratch-yours kind of partnership. Heezen would go out to sea with the other menfolk and gather data; when he returned to his tenured position at Columbia to teach, Tharp would feverishly organize and interpret all the data, using it to create maps of the ocean floor, something that had never been done before. Then, the cycle would start all over again.

Keep in mind that when Tharp started, there was no such thing as a computer as we understand computers today. This meant that Tharp had to develop her own way of interpreting the data, a scheme for drawing the topographical features of the ocean (which did not yet exist), and ink and label it all by hand. She knew she was doing the biggest project of her life, which kept her focussed and motivated.

This went on for years, until Heezen crossed a bigwig at Columbia and was summarily let go. Undeterred, Marie rolled up her maps and took them with her, obtained outside funding and kept working from home. Not only did she keep working on the maps, but she coauthored a book with Heezen and published several scientific papers.

Using sonar and Tharp’s awesome map-making skills, Tharp and Heezen discovered what is now known as the Backbone of the Earth – the Mid-Ocean Ridges that, at 40,000 miles long, are the largest single geographical feature on planet Earth. Tharp’s data showed her a V-shaped gap at the very top of the ridge. When magma emerged from a volcano, it could thrust the earth apart to create such a formation. Therefore, Tharp came to believe that perhaps these ridges had been created by a shifting of the earth’s crust below the ocean, and studied a similar formation on land in Africa to compare them.

The real Marie Tharp, and her picture in the Women in Science game.

The real Marie Tharp, and her picture in the Women in Science game.

The idea that magma could force landmasses to move was “too much like continental drift,” Heezen told her, an idea that was considered radical and therefore unacceptable at the time. Then Heezen actually said aloud that Marie’s ideas were just “girl talk” and ordered her to do the maps again, claiming she must have made some kind of error, like, twenty million times in a row. Remember, this is the woman he worked with for decades, four years his senior and, with a degree in mathematics, more qualified than he to interpret and map the data he’d given her.

Tharp could have tossed Heezen into the ocean, and she’d have had good reason. But it says something about her that she went back to her maps, determined to prove him wrong. Meanwhile, Heezen went off on a solo mission to plot earthquake epicenters on the ocean floor.

But when he returned, he told Marie he had found something incredible: he could lay his map atop Marie’s, and the earthquake epicenters aligned perfectly to the ridges. It now seemed an inescapable idea that earthquakes and the eruption of magma had caused these rifts to spring into being.

In 1957, Heezen presented the findings. Marie did not mind putting her name on publications, but she did not like presenting her findings in public, and in 1950s America, perhaps that was all for the best. “I was so busy making maps,” she said, “I let them argue.

Even with an important masculine figure like Heezen presenting the data, there was still enormous doubt. Jacques Cousteau, the famous underwater explorer, tacked Marie’s map to his ship’s wall, determined to prove it wrong, but his filming of the ocean floor showed Heezen’s gathered data and Marie’s map to be mind-bogglingly accurate.

In 1997, Tharp received double honors from the Library of Congress: she was named one of the four greatest cartographers of the twentieth century, and her works were included in an exhibit of the 100th anniversary of its Geography and Map Division. Her work hung next to the original rough draft of the Declaration of Independence and pages from the exploratory journals of Lewis and Clark. When she saw the map she had labored so many hours to produce displayed in such proud company, she wept.

Barton, C. (2002). Marie Tharp, oceanic 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 (pp. 215-228). London, England: The Geological Society of London.
Bressan, D. (2013, July 30). July 30, 1920: Marie Tharp, the Woman Who Discovered the Backbone of the Earth. Scientific American. Retrieved August 1, 2015, from
Jarvis, B. (2014, December 19). How One Woman’s Discovery Shook the Foundations of Geology. Mental Floss. Retrieved August 1, 2015, from
Tharp, M. (1999). Connect the Dots: Mapping the Seafloor and Discovering the Mid-ocean Ridge. In L. Lippsett (Ed.), Lamont-Doherty Earth Observatory of Columbia Twelve Perspectives on the First Fifty Years 1949-1999 (Chapter Two). Retrieved August 16, 2015, from

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