You might not know her name, but you definitely know her work. When you imagine the ocean floor, it is probably the Marie Tharp map crafted from data collected by Bruce Heezen and other scientists that you see. Even years after the spectacular ocean “topography” gravity maps of Smith and Sandwell in 1997, which show delicate new details, I still see the Tharp-Heezen map in my mind. Placemats with that map have decorated my kitchen table for decades.
Marie Tharp’s maps showed a clear delineation between the continental shelf, slope, rise and the rest of the seafloor, abyssal plains, seamounts and ocean ridges. The area of the continental shelf changes substantially as sea level changes, as do marine depositional environments. As a major key to understanding plate tectonics, her work led to many important developments in identifying offshore drilling targets.
The maps were displayed at the 100th anniversary of the Library of Congress in the Jefferson Building, along with treasures that included a rough draft of the Declaration of Independence, the Emancipation Proclamation and Lewis and Clark’s journals.
Across the Ocean in 80 Days
Tharp created maps that changed the way we imagine two-thirds of the world.
Her hand-drawn renditions of sonar profiles are embedded in the way I visualize a walk across the ocean floor from Washington, D.C. to Casablanca, Morocco. At the brisk pace of 50 miles a day, this 4,000-mile trip – a thousand miles longer than a trip from New York City to San Francisco – would take 80 days. Phileas Fogg, in Jules Verne’s “Around the World in Eighty Days,” got much farther using ships, railroads and even elephants.
The trip would begin by heading south and then southeast down the Potomac River, into the Chesapeake Bay. There, sediment would be very soupy, and maybe something like snowshoes would be needed. Then, just north of Norfolk, head directly west across the continental shelf and slope, but avoid Hudson Canyon. After a short walk along the abyssal plain, I’d travel just south of the New England Seamounts. After these ended, the soft sediment-covered topography would start to get bumpier as I headed up the slope to the Mid-Atlantic Ridge. After a quick traverse through the fresh basalt of the rift valley, I’d be more than halfway. Heading downslope, I’d find my way onto another abyssal plain, much larger than on the eastern side. This terrain would be a relief after the rough ground near the rift valley.
I think the best route to Casablanca would be south of the Canary Islands, then up onto the continental shelf. There is no detail about the outflow from the Oum Er-Rbia (“the mother of springtime” in Arabic) River; probably there were no ship tracks, so this area might be tricky to traverse. Then it would be just about 50 miles to Casablanca.
That’s the kind of detail the Tharp-Heezen maps have, especially in the North Atlantic, where ship tracks were plentiful.
Geoscientists Needed
Marie Tharp’s life is a story of serendipity and relentless persistence. Born in Ypsilanti, Mich., on July 30, 1920, she grew up accompanying her soil scientist father, William Edgar Tharp, into the field. His work for the U.S. Department of Agriculture, Bureau of Chemistry and Soils, meant frequent moves. At the end of high school, she had attended almost two dozen schools in eight states and the District of Columbia.
For college, she enrolled at Ohio University but couldn’t decide on a major. Her search for a major included a geology course, which she loved. She took it late in her undergraduate academic career, probably too late to switch majors. Instead, her bachelor’s degree was awarded in English and music, but she lacked direction. The usual occupations for women in the late 1940s – teacher, nurse, secretary – did not interest her.
The United States was fully involved in World War II by her later years in college. Men were needed in the military and so women were needed for traditionally male jobs. In particular, female geoscientists were needed to replace the men. Although not a science major, she graduated early, and in the winter of 1943 enrolled in a University of Michigan geology master’s program to train women to become petroleum geologists. Two years later, she had the degree and went to work for Stanolind Oil in Tulsa, Okla. As a woman, she was relegated to office work, drafting and transferring data from well logs. She found this boring, so she enrolled in a night program in mathematics at the University of Tulsa, and in 1948 earned a bachelor’s degree.
The Real Story Begins
Tharp was briefly married to a musician. After World War II, he enrolled at Julliard in New York City. Tharp left Tulsa for New York in 1948 to accompany him. That’s when this story really begins. What could a woman with a master’s degree in geoscience do in the post-World War II world of New York City?
Paleontological work at the American Museum of Natural History seemed too tedious, so she sought a job at Columbia University. Entering Columbia’s Geology Department, she was directed to the basement where William Maurice “Doc” Ewing and a group of young male graduate students and a few women were crammed into three rooms – rooms that were previously occupied by the Manhattan Project. She could draft and was hired to assist the male graduate students. Among those students was Bruce Heezen, who had just joined the group.
Marie was assigned to help Heezen, who had been collecting seafloor profiles. These were rolls of data, churned out at a steady rate as a ship traversed the ocean. They showed the depth of the seafloor using early continuous echo sounding to create profiles.
According to Tharp, the profiles were anything but continuous.
“The echo sounder depended on the ship’s electric power, which went off whenever someone opened the ship’s refrigerator,” she said. And navigation, allowing the precise location of the profile, wasn’t very exact. There was no GPS. Nevertheless, between 1946 and 1952, under Ewing’s direction, tens of thousands of measurements were made throughout the ocean, especially the North Atlantic.
In 1949 Columbia University, with Dwight Eisenhower as president, was gifted the Torrey Cliff estate from Florence Corliss Lamont, the widow of Wall Street banker Thomas W. Lamont. This unrestricted gift allowed Columbia University to move the geoscientists from their cramped quarters in Manhattan to a spacious estate overlooking the Hudson River in Palisades, N.Y. Today known as Lamont-Doherty Earth Observatory, it is a geological and oceanographic mecca and was the location for the development of many early marine geophysical instruments.
In their new quarters, now on the second floor of Lamont Hall, Tharp’s drafting continued. It was tedious work. Ships’ tracks were plotted by hand, and then depth profiles were plotted along the ship tracks.
“Eventually, after the plotting, drawing, checking, correcting, redrawing and rechecking were done, I had a hodgepodge of disjointed and disconnected profiles of sections of the North Atlantic floor,” she recounted.
After weeks of reassembling the patchwork of data, Tharp ended up with six west-to-east profiles along the North Atlantic Ocean floor. Her careful plotting revealed something no one had previously described: a cleft in the center of the Atlantic – a “rift valley.”
“When I compared the profiles, I was struck by the fact that the only consistent match-up was a V-shaped indentation in the center of the profiles,” Tharp said. “The individual mountains didn’t match up, but the cleft did, especially in the three northernmost profiles. I thought it might be a rift valley that cut into the ridge at its crest and continued all along its axis.”
When she pointed this out to Heezen, he would have none of it. It was too much like continental drift, which was scientific heresy, and he accused her of “girl talk.” She was told to recalculate and redraft.
She did, but the rift valley was still there.
Shaking the Foundations of Geology
About the same time, Heezen asked her to construct a physiographic diagram of the ocean floor. This would be similar to the one created of the United States by the geomorphologist, A. K. Lobeck. His 1921 “Physiographic Diagram of the United States” was more like an aerial view, giving a sense of the texture of the landscape. This had never been done before for the ocean and, anyway, most people thought that the ocean floor was just flat. A physiographic map had the advantage that it could be published. The U.S. Navy had detailed contour maps, but they were classified at the time.
The data was improving, too. In 1953, Lamont acquired the S.V. Vema, a 202-foot ship, formerly a three-masted luxury schooner built in 1923 for the New York financier, E. F. Hutton. During WWII, the Vema was first used as a coastal patrolling vessel by the Coast Guard but then became a training ship for the U.S. Merchant Marine. All suggestions of past luxury were removed. After the war, the Vema was discarded on Staten Island. The abandoned ship was an opportunity and later rescued by “Doc” Ewing and a Nova Scotian captain.
The masts were removed and the S.V. Vema became the R.V. Vema. (Today, the Vema’s masts have been restored and she sails in the Caribbean as the cruising yacht S.V. Mandalay.)
The repurposed ship was outfitted with new and better equipment for research. A precision depth recorder was installed, providing a more accurate rendition of the seafloor. This allowed Tharp to distinguish more subtle seafloor features, including the ability to identify smooth and rough surfaces. Soon, the R.V. Vema was the first academic research vessel to have a satellite navigation system. (This was nothing like today’s satellites, but as a satellite occasionally passed overhead, the ship’s crew could calculate more accurately their latitude and longitude.)
As Tharp plotted ocean floor depths in Lamont Hall, the adjacent person, a young man, plotted locations of earthquake epicenters on maps at the same horizontal scale. It isn’t clear whether Heezen or Tharp first noticed the correlation. When the maps were compared, the earthquake epicenters plotted inside “her” rift valley. This was a revelation, and soon a revolution. When Heezen, with his new doctorate, gave a talk at Princeton in 1957 showing the rift valley and epicenters, Harry Hess, the department chair, is alleged to have said, “You have shaken the foundations of geology.”
The Valley Was There
Two years later in 1959, the Geological Society of America published “The Floors of the Oceans: I. North Atlantic,” by Heezen, Tharp and Ewing. It contained her profiles and physiographic maps. Some called it “nonsense,” others “brilliant,” but most didn’t believe it.
Jacques Cousteau was determined to prove her wrong. Sailing aboard the Calypso to the United Nations to attend the First International Oceanography Conference, he paused midway. There he lowered his underwater movie camera with 16-millimeter film and planned to show no valley. He was wrong. The valley was there.
Why the valley was there posed another problem. Some ideas were proposed by Harry Hess in a paper published by the Geological Society of America in 1962, one of the seminal papers in the development of plate tectonic theory. It failed to reference the critical work presented in “The Floors of the Ocean,” one of the few publications that included Tharp as a co-author. Unlike Heezen and Ewing, who had many research interests and publications, Tharp was solely focused on bringing the ocean floor to life.
Her Rightful Place Among the Giants of Discovery
National Geographic published her Indian Ocean map in October 1967, providing their millions of subscribers access to this view of the ocean floor. The collaboration between National Geographic, Tharp and Heezen continued for 10 more years, ending with the publication of the 1977 World Ocean Map, now in the Library of Congress.
That same year, Heezen had a fatal heart attack aboard a research submersible in the North Atlantic. In October 1978, Heezen (posthumously) and Tharp were awarded the Hubbard Medal, National Geographic Society’s highest honor, and they joined the ranks of Ernest Shackleton, Louis and Mary Leakey, and Jane Goodall.
Today, seafloor mapping by ships is done using swath mapping, which creates a ribbon rather than a knife view. Like mowing the lawn, the ribbons can be stitched together to create a comprehensive map. The problem is that ships move slowly. It would take one ship 200 years to map the entire seafloor. More ships are needed. Today there’s a multinational effort led by the Nippon Foundation and the General Bathymetric Chart of the Oceans to map the entire ocean floor in detail by 2030. This might seem an obscure pursuit, but the ocean is the source of tsunamis. The seafloor provides habitat for an extensive marine ecosystem, and the topography controls currents that distribute heat and nutrients.
Marie Tharp died of cancer in Nyack, N.Y. on Aug, 26, 2006 at the age of 86. She was a longtime resident of South Nyack, just a few miles north of LDEO.
The 1977 Tharp-Heezen ocean seafloor maps showed the main features of the seafloor and where they are located. Her name should be as well known to us as Jane Goodall and Neil Armstrong. Fortunately, an effort led by Phoebe Cohen of Williams College will help us to popularize her contribution: Marie Tharp mugs. I have two dozen and am giving them to my research students so that they and I can begin a conversation about this remarkable woman.
Learn more about Marie Tharp in Hali Felt’s “Soundings.”