Saturday, May 14, 2016

Marie Tharp, Cartographer

Marie in 2001, photo by Bruce Gilbert

Marie Tharp was the first to map the ocean floor and prove the existence of mid-ocean ridges, a theory that had been refuted for decades. This led to the acceptance of the now fundamental concepts of plate tectonics and continental drift.

"I was so busy making maps I let them argue... there's truth to the old cliche that a picture is worth a thousand words and that seeing is believing." ~ Marie Tharp

Marie Tharp was born in Ypsilanti, Michigan, in 1920. Her mother was a teacher of Geman and Latin, and her father was a soil surveyor for the Federal Bureau of Chemistry and Soils. Marie adopted the interests of her parents at an early age, as she would accompany her father on field trips to take soil samples, and would later consider being a teacher.

Her father's job meant  that the family had to move frequently, and Marie attended twenty different public schools in six states. After her father retired in 1931 the family settled in Ohio, where Marie graduated from high school.

A woman of many interests

Marie enrolled at the University of Ohio but had not decided on a major. Her father's advice was to pick a subject she liked, and that would become the way she earned a living. Every semester Marie picked a new major to pursue, though her choices were limited as not every major was open to women - the sciences were men only, for example. In 1943, she graduated with a bachelor's degree in music and English, and four minors.

It was at the University of Ohio that Marie discovered geology, and found a mentor who encouraged her to take drafting, as it might help her get a job in an office (fieldwork was out of the question for women).

While still completing her degree, Marie found a pamphlet about the graduate geology program at the University of Michigan. The university, which had never allowed women to enter its graduate program, was now facing empty classrooms as all the young men were engaged in the war effort, and it was appealing to young women to apply.

Marie jumped at the chance and enrolled in the accelerated geography degree. She became enthralled with geomorphology, the science of how landscapes form. After graduating with a master's degree in 1944, Marie went to work as a junior geologist at an oil company in Tulsa, Oklahoma. Denied the opportunity to do field work due to her gender, Marie staying the office coordinating the maps and data of her male colleagues, who were off collecting it. She reported being "bored as hell" during that time, but she put the years to good use and earned another bachelor's degree in math in 1948.

Onward and Eastward

Desperate for a new opportunity, Marie left Tulsa after four years with the oil company and headed to Columbia University. There she found a position as research assistant to geology graduate student Bruce Heezen. Such was the beginning of what would be a nearly thirty year collaboration and a relationship that was both personal and professional, though it was never confirmed to be romantic.

It was the early 1950s, and there was great interest in understanding the nature of the ocean's floor (as there had been during the war), for this data would be useful for anti-submarine warfare. After the advent of sonar, navy submarines were outfitted with instruments to send a receive "pings" that would tell them the depth of the water below them. These measurements were recorded and were the initial data set from which Heezen's team began to map the ocean.

To gather additional data, Heezen and Maria's other male colleagues took to the seas, crisscrossing the oceans on ships and recording their findings. Women were considered bad luck on ships, so Maria stayed in the lab, checking and plotting the ships' findings meticulously by hand.

At the drafting table, Columbia
By 1952, Heezen's team had tens of thousands of measurements, still an infinitesimal amount considering how much of the ocean was left uncharted. Maria spent weeks on her mapping, creating six parallel profiles of the Atlantic floor, stretching from east to west. It was not just a matter of taking the data and using it to mark her map; as the data was incomplete, Marie had to use her understanding of geology to make an educated deduction of what the sea floor looked like between the measurements.

The profiles revealed underwater landscapes that had never previously been known or understood: continental shelfs rising from the abyss, and mountain ranges on the ocean floor. In addition, there were deep V-like notches running the entire length of the mountain ranges.

When Maria looked at those notches, she recognized them - them immediately went back to check her data, assuming it had been a mistake. It would be the same reaction Heezen would have weeks later. But the notches were no mistake.

Since the 1800s, theories of the ocean floor

The earliest measurements of the ocean floor were scattered recordings, usually by government-sponsored expeditions. One Atlantic expedition in the 1870s exploring the depths with the intent of lying transcontinental telegraph cables stumbled upon a mountain range, but this so perplexed the scientific community that it was thought to be a mistake, and left unexplained. The sea was considered a great unknowable mystery, and the bottom was presumed to be flat.

All this until the 1900s, when a German geologist named Alfred Wegener put forward the theory of continental drift: that the Earth's continents had been all connected at one time, and then drifted apart.

For this theory, he was laughed at and mocked; at a gathering of the American Association of Petroleum Geologists in 1926, the idea was rejected on the grounds that no force on earth was deemed powerful enough to move continents. "The dream of a great poet," declared the director of the Geological Survey of France.

In the meantime, expeditions by the German Meteor from 1925-1927 revealed a landscape that would be called the Mid-Atlantic Ridge, confirming the findings of the British HMS Challenger in the 1870s. Overall however, the ocean floor remained unmeasured, and the theory of continental drift was dismissed as "poppycock." You could even get fired for believing in it, Marie would later recall.

But Marie had faith in her numbers, and as she examined her own charted profiles and the deep notch that ran the entire length of the mountain range on the ocean floor, she knew it looked too much like a rift valley - a spot where two masses of land had separated - to be ignored.

Rift Valley making rifts

When Maria showed her maps to research supervisor Heezen, he refused to accept them. "It cannot be," he told her. "It looks too much like continental drift." Telling Maria her interpretation of the maps was "girl talk" and worried about the reputation of his lab, he told Maria to go back and chart everything again.

While Maria charted everything again from scratch, Heezen worked on another project, this one for a cable company looking for safe places to run transcontinental cables. As he compiled the data he created his own map, this one showing the epicenters of earthquakes on the ocean floor. Surveying the results, Heezen noticed something strange: the majority of earthquakes occurred along a nearly continuous line that ran across the Atlantic.

When he lined his map up with the new one Maria had created (which showed findings identical to the first), the two maps correlated - the earthquakes lined up along the Mid-Atlantic ridge.

Marie with her lifetime associate, Heezen
The couple moved on to other oceans and expeditions, and saw that the pattern kept repeating. They mapped out further mountain ranges, all connected and split in the middle by rift valleys, and along all of them, they found the same evidence for high occurrence of earthquakes.

Wrote Tharp, "There was but one conclusion. The mountain range with its central valley was more or less a continuous feature across the face of the earth." While the two could not agree on whether this provided concrete evidence of continental drift, some results were indisputable, like the 40,000 mile-long mountain range underwater that wraps around the entire earth. This geographical feature remains the largest one on Earth.

World Ocean Floor Panorama, 1977, Marie Tharp and Bruce Heezen.
Credit to Marie Tharp Maps, New York
Going Public

In 1957 Heezen took the pair's findings public, to mixed results - Tharp would later describe the reaction as ranging from "amazement, to skepticism, to scorn." As for Heezen, he was still disbelieving that the ranges and rifts provided evidence of continental drift, and he never fully acknowledged Tharp's contribution to the project. 

The theory got a boost in 1959, however, when Jaques Cousteau, formerly a doubter, pinned Marie's maps to the wall of his ship and went out the Mid-Atlantic Ridge to do some filming there. What he found shocked him, as brought back from a camera on a sled that he had navigated along the sea floor was footage showing the mountains and rifts in locations corresponding exactly with Marie's map.

Cousteau screened this footage at the International Oceanographic Congress in 1959, and the audience gasped and cheered. The rift that Marie had charted with the data gathered from the team in the field was real.

Heezen, however, was still skeptical, and presented a paper that same year proposing a theory as to how the rift was created. Other hypotheses abounded as the field of geology scrambled to find an explanation for the formation of the earth's surface, but nothing was convincing. As usual, Marie stayed out of the spotlight, choosing to keep working instead and let the evidence speak for her.

In private, the arguments between Heezen and Marie could be epic, with Heezen kicking trash cans and  throwing map weights in frustration. While he finally came over the Marie's side and agreed that the rift in the valley was caused by land masses pulling apart, their supervisor still disagreed, and  was so furious he fired Marie. 

Public Acceptance

By 1961 the idea Marie came up with nine years prior finally reached public acceptance, and Marie and Heezen were commissioned by the National Geographic Society to make a map of the ocean floor and its features. Throughout the 1960, this map and additional discoveries led to the acceptance of such concepts as seafloor spreading and plate tectonics, as the general public began for the first time to grasp the notion of what was going on in the underwater world they could not see.

Still banned from going on research cruises, Marie was only able to go on board a ship to sail over the terrain she charted in 1967. She would not receive full recognition of her work until 1997, when the Library of Congress named her one of the four greatest cartographers of the 20th century, and included her work in an exhibit in its Geography and Map division, where it hung near the first draft of the Declaration of Independence and pages from the journals of Lewis and Clark.

When Marie saw her map hanging there, she started to cry. She had always known the significance of the discovery, even when no-one else believed it. "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 later wrote. “You could only do that once. You can’t find anything bigger than that, at least on this planet."

Sources:
  • How One Woman's Discovery Shook the Foundations of Geology, Brook Jarvis, Mental Floss, mentalfloss.com, December 2014
  • Headstrong: 52 Women who Changed Science - and the World. Rachel Swaby, Broadway Books, 2015
  • Floating Ideas, Michael Washburn, New York Times, www.nytimes.com, January 25th, 2013

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