Women in Earth Science: Marie Tharp (1920 - 2006)
Marie Tharp was a 20th century Geologist from the United States who created the first scientific map of the Atlantic Ocean floor, as well as prove continental drift was real.
As a student, Tharp had struggled to find the right university major; she wanted something she could do, and enjoy, but there were not many options for women in her day. More opportunities opened up during WWII and she took the chance to return to school and study geology and then math.
Tharp spent months painstakingly "plotting, drawing, checking, correcting, redrawing and rechecking" profiles of the North Atlantic. The ship tracks across the Atlantic were a sparse web, but when Tharp compared half a dozen more or less parallel transects, she noticed not only the general similarities of the ridge, but a V-shaped notch in the centre of all the profiles. She suspected they coincided because they indicated a rift valley all along the ridge crest. The early ideas about plate tectonics or the "continental drift" theory were still quite controversial and unpopular. Bruce Heezen, her academic partner at the time, dismissed Tharp's observation as "girl talk" for looking too much like continent drift! In fact it was indeed a vital piece of the plate tectonics puzzle.
Though her contour maps hadn't convinced Heezen, Tharp believed the rift was real. In 1952, they began working on physiographic maps, which would show seafloor topography as if you were flying just above it, and the water were drained away. The precision of depth recorder data was increasing, which revealed far more features, and better navigation allowed her to plot ships' positions along tracks more accurately. A second project in their research group involved plotting earthquakes, and Heezen insisted they produce maps at the same scale. Heezen then noticed that ocean earthquake epicentre data also formed long lines - and in fact, when one map was placed above the other on a light table they found the earthquakes formed near continuous lines right along the Mid-Atlantic ridge right where Tharp had indicated there was a rift valley. Using the earthquake data to extrapolate and plot the rift position, they found that the rift extend landward into the Rift Valley of East Africa - a well-known, easy to observe terrestrial rift valley. Heezen was finally convinced. They had discovered a worldwide mid-ocean ridge system, tens of thousands of kilometres long. Ewing and Heezen announced their findings in 1956. In 1957 Tharp and Heezen published their North Atlantic physiographic map.
They continued this work, extending to other oceans over the next 25 years, ultimately producing detailed physiographic maps of the world oceans. Their pioneering work mapping the oceanic plate boundaries, and showing their clear alignment with seismic data helped fuel the revolution in geology and geophysics, the paradigm shift of plate tectonics.
Tharp's work was largely in the background during her university career, though she won a number of prizes during her retirement and has continued to gain posthumous recognition for the importance of her work and observations. I was very pleased to see her recognized recently in Neil DeGrasse Tyson's Cosmos reboot. I want to bring her incredible insight and excellent work to a wider audience as both artist and marine geophysicist myself!
There are now a lot of good references for Marie Tharp on the web. Her own acceptance speech for the Mary Sears Woman in Oceanography Award tells the story of her discovery of the mid-ocean ridge in her own words. Despite being a marine geophysicist, Tharp came to my attention when I read her obituary in the New York Times. There’s a lovely short animated film about her made by the Royal Institution here.
You can find a brief summary of her life and achievements on her Wikipedia page or read her full biography by Hali Felt (2012). Soundings: The Story of the Remarkable Woman Who Mapped the Ocean Floor. New York: Henry Holt and Co. ISBN 9780805092158. Find my own portrait of Marie Tharp here.
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