On June 29, 1957, Marie Tharp published the first detailed physiographic map of the Atlantic Ocean floor, created in collaboration with Bruce Heezen at the Lamont Geological Observatory.

The map showed, for the first time, the mid-Atlantic Ridge — a continuous mountain chain running down the center of the Atlantic, with a rift valley at its crest.

Tharp immediately recognized what it meant. The rift valley matched the pattern predicted by continental drift theory — then still considered fringe science. She told Heezen. He told her she was speaking "girl talk."

She collected the evidence anyway, correlating the topographic data with earthquake records, showing that the earthquakes clustered precisely along the rift valley. Heezen became convinced. The paper they published helped trigger the revolution in earth sciences that became plate tectonics.

Tharp had not been allowed on the research ships. Women were considered bad luck at sea in the 1950s. She worked from the data that the ships brought back, converting the sonar readings into maps by hand.

Heezen received most of the scientific credit for the discovery during his lifetime. After his death in 1977, the record was slowly corrected. The Library of Congress named Tharp one of the greatest cartographers of the 20th century in 1997.