Until Marie Tharp came along, no one knew what the seafloor really looked like.

It was long thought to be a featureless plain of mud.

Then sonar, invented in World War II, began to give us a glimpse. But it could only “read” the bottom of the ocean right below the ship’s path.

Marie Tharp earned master’s degrees in geology and mathematics in the 1940’s and joined the navy to study the seafloor—but women were not allowed on research ships.

Instead, she was assigned to process and analyze new sonar data from hundreds of voyages.

She soon discovered a deep rift valley in the Atlantic Ocean, which suggested the ocean floor was expanding. But other scientists rejected the idea.

By coincidence, Howard Foster, stationed at the next desk, was plotting undersea earthquake areas to avoid for a transatlantic cable. His fault zones lined up almost exactly with Tharp’s mid-Atlantic trench. They became convinced it was an active geological boundary.

But the concept of plate tectonics was then so controversial that Tharp was fired. Undaunted, she continued to work from home.

In the 1960’s, she and Dr. Bruce Heezen finally presented their combined data to the scientific community, displaying their new undersea topographic maps in spectacular color.

Their work convinced the naysayers and has changed the way that people view and understand global geology.