Who mapped the seafloor when women were barred from research ships?

Marie Tharp did, working from other people's depth measurements. In the 1950s she and the geologist Bruce Heezen produced the first scientific map of the Atlantic Ocean floor. Heezen collected the data at sea; Tharp drew the maps. For the first 18 years of their collaboration she did not go on the ships, because women were barred from working on them. She joined an expedition only in 1968.

It was not her first closed door. At her first job, at an oil company in Tulsa, she found that women were not permitted to do or attend fieldwork. She moved to New York and was hired to do drafting work with Maurice Ewing, founder of the Lamont Geological Observatory. At the interview, she did not mention her master's degree in geology.

Her key moment came in 1952. Lining up sounding profiles of the North Atlantic, she found an aligned V-shaped structure along the axis of the ridge and thought it might be a rift valley formed by the ocean floor being pulled apart. Heezen was unconvinced, because the idea would have supported continental drift, then a controversial theory. He dismissed her explanation as "girl talk". Then a map of earthquake epicentres was overlaid on her profile, and the earthquakes lined up with her rift valley. Only after seeing that did Heezen accept her hypothesis and turn to plate tectonics and continental drift.

Tharp then showed the valley continues into the South Atlantic, and found similar valleys in the Indian Ocean, the Arabian Sea, the Red Sea and the Gulf of Aden. The result was the first map of the whole ocean floor, published by National Geographic in 1977. In 1997 the Library of Congress named her one of the four greatest cartographers of the 20th century.