Mary Tharp helped map the ocean floor that, 100 years after her birth, should be recognized as one of the greats of science.

July 30 marks the centenary of the birth of Mary Tharp, a geologist and oceanographer who created maps that changed the way people imagine two-thirds of the world. Beginning in 1957, Tharp and her research partner, geologist Bruce Heezen, began publishing the first comprehensive maps that showed the main features of the ocean floor – mountains, valleys, and trenches.

As a geologist, I think Tharp should be as famous as Jane Goodall or Neil Armstrong. Here’s why.

Crossing the Atlantic Ocean

In the 1950s, many scientists assumed that the sea floor was virtually flat. Tharp showed that it has rugged terrain, and a large portion of it has been designed in a systematic way.

Its images were crucial in developing the theory of plate tectonics – the idea that plates, or large parts of Earth’s crust, interact to generate the planet’s seismic and volcanic activity. Previous researchers – especially geophysicist and meteorologist Alfred Wegener – observed how closely the coasts of Africa and South America fit together and suggested that the continents were once connected. Tharp identified the mountains and a rift valley in the middle of the Atlantic where the two continents would have separated.

Thanks to Tharp’s hand-drawn ocean floor renditions, I can envision walking across the bottom of the Atlantic from New York to Lisbon. The journey was taking me along the continental shelf. Then down to the Abyssal Plain of Som. I’ll need to get around the underwater mountains, which are called seamounts. Then I start a slow climb over the Mid-Atlantic Ridge, a mountain range submerged between north and south.

After climbing 8,200 feet below sea level to the top of the hills, I would descend several hundred feet, cross the central rift valley of the hills and advance uphill over the eastern edge of the hills. Then back to the ocean floor, until I started climbing the European continental slope to Lisbon. The total walk will be approximately 3,800 miles – nearly twice the length of the Appalachian Trail.

Unseen mapping

Tharp was born in Ypsilanti, Michigan and studied English and music in college. But then in 1943 she enrolled in a master’s degree program at the University of Michigan designed to train women to become petroleum geologists during World War II.

Tharp later recalls: “Girls were needed to fill jobs that were left open because men were out of the fight.”

After working for an oil company in Oklahoma, Tharp sought a job in geology at Columbia University in 1948. Women couldn’t go on research ships, but Tharp could enlist, and she was hired to help male graduate students.

Tharp worked with Heezen, a graduate student who gave her seabed profiles for formulation. These are long paper rolls showing the depth of the sea floor along a linear path, measured from a ship using sonar.

Starting with a large blank sheet of paper, select Tharp’s lines of latitude and longitude. Then she carefully determined where the ship traveled. Next, I read the depth at each location away from the sonar profile, mark it on the ship’s path and create its own condensate profile, showing the depth to the ocean floor versus the ship’s distance.

One of its important innovations was the creation of diagrams that depicted the shape of the sea floor. These views made it easy to visualize the topography of the ocean floor and create a physiographic map.

Tharp’s meticulous mapping of six contours from east to west across the North Atlantic revealed something that no one had described before: a rift in the middle of the ocean, miles wide and hundreds of feet deep. Tharp suggested that it was a rift valley – a type of long basin known to exist on Earth.

Another research assistant was plotting epicenter locations on a map of the same size and scale. Comparing the two maps, Heezen and Tharp realized that the epicenter of the earthquake fell within the Rift Valley. This discovery was crucial to the development of plate tectonics: it suggested that movement was occurring in the Rift Valley, and that the continents might actually drift apart.

This insight was revolutionary. When Heisen, as a recent Ph.D., gave a lecture at Princeton University in 1957 showing rift valley and earthquake centers, geology chief Harry Hess replied, “It shook the foundations of geology.”

Tectonic resistance

In 1959, the American Geological Society published “Floors of the Oceans: I. North Atlantic Ocean,” by Heisen, Tarb, and Maurice “Doc” Ewing, director of the Lamont Geological Observatory, where they worked. It contained Tharp’s ocean profiles, ideas, and access to Tharp’s physiological maps.

Some scholars thought the work was cool, but most of them didn’t believe it. French undersea explorer Jacques Cousteau was determined to prove Tharp wrong. He sailed aboard his research ship, the Calypso, intentionally crossed the ridge in the mid-Atlantic and launched an underwater film camera. To Cousteau’s surprise, the film showed the existence of a rift valley.

Tharp noted in a 1999 retrospective article: “There is truth in the old cliché that a picture is worth a thousand words and that a vision is a belief.”

What could create a rift? Hess proposed some ideas in a 1962 paper. I assumed that hot magma rose from within the Earth at the rift, expanding as it cooled and pushing two adjacent plates away from each other. This idea was a major contribution to plate tectonics, but Hess fails to refer to the critical work presented in The Floors of the Oceans – one of the few publications that includes Tharp as a co-author.

Still scanning

Tharp continued to work with Heezen to bring the ocean floor to life. Their collaborations included the Map of the Indian Ocean, published by National Geographic in 1967, and the 1977 Floor Map of the World Ocean which is now kept in the Library of Congress.

After Heezen’s death in 1977, Tharp continued her work until her death in 2006. In October 1978, Heezen (posthumously) and Tharp were awarded the Hubbard Medal, the highest honor from the National Geographic Society, and joined the ranks of explorers and explorers such as Ernest Shackleton, Lewis Mary Leakey and Jane Goodall.

Today, ships use a method called mapping, which measures depth over a tape-like path rather than the length of a single line. The strips can be stitched together to create an accurate map of the sea floor.

But because ships are moving slowly, it could take 200 years to fully map the sea floor. An international effort is underway to map the entire ocean floor in detail by 2030, using multiple ships, led by the Nippon Foundation and the General Ocean Depths Planner.

This information is essential to begin to understand what the sea floor looks like on a neighborhood scale. Tharp was the first person to demonstrate the rich terrain of the ocean floor and its various biomes.

Susan O’Connell is Professor of Earth and Environmental Sciences at Wesleyan University. This article was originally published on theconversation.com.

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