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17

Mar

2021

Marie Tharp: discovered the Rift Valley in the Mid-Atlantic Ridge

Written by: Simon Mitton

 
Marie Tharp’s transatlantic profiles with her annotations of the Mid-Atlantic Ridge and its central valley. Acknowledgement: US Library of Congress. Simon Mitton.
 

Marie Tharp’s transatlantic profiles with her annotations of the Mid-Atlantic Ridge and its central valley.
Acknowledgement:  US Library of Congress. Simon Mitton.


In this post on “deep carbon science” –– a fascinating research field in the geosciences –– I recount the research of Marie Tharp (1920–2006) a great pioneer in visualizing the geology of the ocean floor. She majored in English and music at the Ohio University in 1943, and then became a wartime recruit to a petroleum geology program at the University of Michigan, where she received her master’s degree. Her transition to geoscience was extraordinary at the time: women had long been discouraged from working in the field. Although she joined a petroleum company as a junior geologist, charged with the analysis maps and field data, she disliked being shut indoors on office work.

Following a move to New York in 1948, she was engaged by the Lamont Geological Observatory of Columbia University, being one of the first women scientists they employed. As a shore-based assistant she drafted oceanographic maps for the Observatory’s first director, Maurice Ewing (1906–1974), a renowned seismologist skilled at the use of sound waves for mapping the ocean floor. Ewing was ruthlessly determined to maximise the scientific output of his research team and its ship. Lamont led the world as a tidal wave of geoscience data flooded into the observatory.

Back in 1852 an American warship, USS Dolphin had carried out the depth soundings in the Mid-Atlantic that first revealed a shallow zone, later named the Mid-Atlantic Ridge. Tharp’s role at Lamont was to transform transatlantic depth profiles from the sounding data into highly detailed profiles of the floor of the North Atlantic. She became struck by the similarities of shape evident in half a dozen profiles. When she scrutinised three these, she spied a single V-shaped notch that made a good match across the trio of profiles. Her immediate thought was “it might be a continuous rift valley that cuts into the ridge at its crest and continues all along its axis.” She pointed this out to her manager Bruce Heezen who advised, “It cannot be. It looks too much like continental drift.”

In that era, the early 1950s, continental drift was still regarded in the USA as scientific heresy. Heezen and Ewing continued to believe that the major geophysical features in the oceans were the consequences of the expansion of the Earth! Many years later Bruce admitted that in 1952, “I discounted it as girl talk and didn’t believe it for a year.”

Legacy: In 1997 the Library of Congress named Marie Tharp as one of the four greatest cartographers of the twentieth century. In 2015 the International Astronomical Union named a lunar crater Tharp in her honour.


Read much more about Marie Tharp, pioneer cartographer of the ocean floor in … Simon Mitton, From Crust to Core 9781108426695, 167–193.
Next time: William Gilbert (1544–1603), the Elizabethan pioneer of geomagnetism.

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About the Author: Simon Mitton

Simon Mitton is a Life Fellow at St Edmund's College, University of Cambridge. For more than fifty years he has passionately engaged in bringing discoveries in astronomy and cosmology to the general public. He is a Fellow of the Royal Historical Society, a former Vice-President of the Royal Astronomical Society, and a Fellow of the Geological Socie...

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