The Woman Who Mapped The Seafloor

(From the 8/23/19 show) Let’s talk about plate tectonics. It’s a truly fascinating story with an amazing woman planted directly in its center. It starts in 1926 when a german meteorologist named Alfred Wegener told a gathering at the American Association of Petroleum Geologists that he believed that the continents had once been locked together and then drifted apart from one another to the configuration we see today.

He was pretty much laughed out of the room. His colleagues assured him that there was no force that would be powerful enough to move continents. “The dream of a great poet,” opined the director of the Geological Survey of France: “One tries to embrace it, and finds that he has in his arms a little vapor or smoke.” William Berryman Scott, then president of the American Philosophical Society called it “Utter damned rot!” The geologist Philip Lake suggested that “Wegener is not seeking the truth, he is advocating a cause and is blind to every argument and fact that tells against it.” There was one glaring problem at the time… there was indeed no plausible mechanism for how this movement might happen. But it has been suggested that two other factors played an even larger part in the rejection… Wegener was a german and in post-WWII America there was still much animosity towards the Germans and he was also a meteorologist rather than a geologist. The rejection of his theory led to many setbacks in his career but he carried on. He died rather heroically during an expedition in Greenland. Having set out to deliver supplies to a team facing starvation who were stranded in the middle of winter he apparently died of a heart attack on the way back to base camp.

It fell to later researchers to find the missing mechanism and to restore the intellectual honor of Wegener. That mechanism was found beneath the waves. I’ve mentioned before that the oceans are fairly mysterious still.  We’ve mapped a fraction of the ocean floor-scientists estimate that only 10 to 15 percent has been mapped in detail. And yet, as you know, the entire planet is 70% oceans! However, there was one woman who worked hard to change this fact.

Marie Tharp was born in 1920 in Michigan. Tharp became a geologist and cartographer and together with her research supervisor Bruce Heezen (four years her junior), she was the first to scientifically map the ocean floor. As a child she would join her father, who worked for the Bureau of chemistry and soils, as he collected samples. She began her career in the 1940s when women were generally not welcomed in the field of geology but with the start of WWII women were afforded access to many areas that had once been unavailable. While at the University of Ohio Tharp’s mentor had encouraged her to take up drafting. With fieldwork still largely unavailable to men it would give her a skill to attract better job offers. After Ohio she went on to earn a degree in Mathematics at the University of Michigan. In 1948 she moved to Columbia University’s Lamont Geological Laboratory (now the Lamont-Doherty Earth Observatory) where she met Bruce Heezen and began on two projects-one to locate downed WWII aircraft and the other to create a topographic map of the ocean floor.

It would be this mapping that would change the face of geology and earth sciences. Up until this era, most scientists assumed the ocean floor was a featureless plain of mud. No serious mapping had been done and with the technology available it was hard to image any large amount of the seafloor. The topography project would become their principal endeavor and they worked on it through the 50s into the 70s. Heezen would go out on research vessels and collect data. Most of this was sonar measurements. As you probably know, sonar devices send out sound waves that bounce off of objects and are reflected back to a microphone set up to record them. The process on board involved sending out ‘pings’ at regular intervals which would be picked up by a microphone on the ship which was attached to a stylus which would make marks on a recording paper. Due to improvements in the technology the apparatus could make continuous readings. Of course Heezen had to be the one to gather the raw data because women were not allowed on ocean vessels at this time because the lab director considered them bad luck at sea. Not surprising given the seeming ubiquity of superstitious seamen.

But this was actually fine because it gave Tharp the ability to turn the data-printed on 5000 foot long scrolls-into systematic maps of the ocean floor. Tharp used her drafting skills to transform the scribbles using pen, ink and rulers on sheets of white linen, into actual pictorial representations of the seafloor. She used a technique called physiographic mapping which uses light and texture instead of color to create her maps. She also integrated research data from other sources including Woods Hole Oceanographic Institution and from seismographs of underwater earthquakes. 

Tharp’s maps revealed that the world’s ocean was just as varied as that of the continents with valleys, mountains, and volcanoes and often these features were much larger and more dramatic than those found on land. Tharp stated that the work was made more exciting due to the fact that she had been working with what was essentially a blank canvas. One must note that there were some inklings that there was something more out there…in the 1870s an expedition testing routes for the transatlantic telegraph cables had been shocked to discover a mountain range in the middle of the Atlantic.

Tharp’s maps showed for the first time exactly where the continental shelf began to rise out of the abyssal plain. It was in 1952 that Tharp found that feature-a chain of mountains and volcanoes that runs north to south in the middle of the Atlantic ocean-now called the Mid-Atlantic Ridge. Importantly she also found a depression “a deep notch near the crest of the ridge” that ran the entire length of the ridge. At first she believed it to be a mistake and doubled and then triple-checked her work. She knew she’d found a rift valley under the ocean. The only problem was that she knew it would be an incredibly hard thing to convince others of her finding. Plate tectonics and continental drift were still considered verboten topics. When she showed Heezen “he groaned and said, “It cannot be. It looks too much like continental drift,’” Tharp wrote later. “Bruce initially dismissed my interpretation of the profiles as ‘girl talk.’” With the lab’s reputation on the line, Heezen ordered her to redo the map. Tharp went back to the data and started plotting again from scratch.

In late 1952, as Tharp was working on this replotting of her map, Heezen took on another challenge which meant he needed to create a map of his own. He was searching for safe places to plant transatlantic cables. By plotting earthquake epicenters in the ocean floor he began to notice something strange, most quakes occurred along a continuous line that sliced down the center of the Atlantic. When he compared his map to Tharp’s newly replotted map, he realized that this line corresponded almost exactly with Tharp’s rift valley. Their work had revealed 40,000 miles of underwater ridge that ran throughout the globe.

In 1957 Heezen took some of the findings to the public. Tharp would later recall that the reactions “ranged from amazement to skepticism to scorn.” One of those who reacted with scorn was the venerable oceanographer Jacques Cousteau. Cousteau began filming the Atlantic Ocean’s floor and was determined to prove Tharp’s theory wrong. He tacked her map to the wall in the ship’s mess hall. Of course, once Cousteau reached the ridge, his footage proved Tharp’s theory without a doubt. He was so astonished he ordered the ship to turn around and return to film again. In 1959 Cousteau screened the video at the International Oceanographic Congress. The audience gasped and shouted for an encore. But the theory was still to be accepted.

In 1959, Heezen, presented a paper endorsing the theory of the Expanding Earth. This posited that the continents were moving as the planet expanded. Other hypotheses joined in the fray. Tharp stayed out of it. She preferred to continue with her work. She consented to present a paper only once, on the condition that a male colleague do all the talking. “There’s truth to the old cliché that a picture is worth a thousand words and that seeing is believing,” she wrote. “I was so busy making maps I let them argue. I figured I’d show them a picture of where the rift valley was and where it pulled apart.” Eventually, by the early 60’s, Wegener’s once radical view came to be accepted by the majority of geologists and oceanographers. Tharp compared the collective eye-opening to the Copernican revolution. “Scientists and the general public,” she wrote, “got their first relatively realistic image of a vast part of the planet that they could never see.” And in 1961 she finally managed to see it herself. Heezen arranged for her to join a research cruise even though women were still not welcome.

They issued their first completed map of the North Atlantic in 1957, followed by maps of the South Atlantic and Indian Ocean in the 60’s. Heezen died in 1977. That same year Tharp published a comprehensive map of the entire ocean called the World Ocean Floor Map. In 1997, freed from Heezen’s shadow, Tharp received double honors from the Library of Congress. She was named one of the four greatest cartographers of the 20th century and featured one of her maps of the ocean in their 100th anniversary of the geography and map division. Her map hung in the company of the original rough draft of the Declaration of Independence and pages from Lewis and Clark’s journals. When she saw it, she cried. “Establishing the rift valley and the mid-ocean ridge that went all the way around the world for 40,000 miles—that was something important,” she wrote. “You could only do that once. You can’t find anything bigger than that, at least on this planet.” She continued to work at Columbia University until her death in August of 2006.

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