Picture This: A Tectonic Revolution

Let’s file this one under “Profiles of Pioneering Women in Science.” For Pioneer Works’ Broadcast, Elise Cutts highlights the work of geologist Marie Tharp, whose maps of the seafloor transformed our understanding of Earth. Her discovery of the Mid-Atlantic Ridge sparked a scientific revolution, leading to the acceptance of the theories of plate tectonics and continental drift. Cutts documents a chapter in the history of Earth science and honors a scientist who made incredible contributions to the field despite the sexism she faced.

A trained geologist, Tharp knew immediately what she was looking at. It was a rift valley—a dip in the Earth formed as its surface pulls apart.

At first, Heezen dismissed Tharp’s interpretation as impossible “girl talk.” If the Earth’s surface was pulling apart from the Mid-Atlantic Ridge, the continents on either side of the Atlantic would presumably be drifting apart—and continental drift was, at the time, tantamount to scientific heresy. But Tharp was confident she was right and Heezen came around eventually. In 1952, he had her begin work on a full map of the North Atlantic seafloor. In parallel, Heezen hired a graduate student to plot the epicenters of undersea earthquakes on a map of the same scale as Tharp’s. With the two maps layered over each other on a light table, the earthquake epicenters ran right down Tharp’s V-shaped valley. Further expeditions revealed that the Mid-Atlantic Ridge extended into the Indian Ocean and into the East African Rift on land, and Heezen concluded that the Atlantic ridge must be just one arm of an enormous, 40,000-mile rift system spanning the entire globe.