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Obituaries

Marie Tharp, 86; Pioneering Maps Altered Views on Seafloor Geology

September 04, 2006|Valerie J. Nelson | Times Staff Writer

Marie Tharp, an oceanographic cartographer who drew pioneering maps of the world's oceans and whose observations from the late 1950s through the 1970s helped scientists reconsider the geology of the seafloor, has died. She was 86.

Tharp died of cancer Aug. 23 at Nyack Hospital in Nyack, N.Y. The death was announced by Lamont-Doherty Earth Observatory of Columbia University, where she had worked from 1948 until retiring in 1982.

With longtime collaborator Bruce Heezen, Tharp published her best-known work -- the first global map of the bottom of Earth's oceans -- in 1977.

The groundbreaking map unmasked a dark world of deep canyons, impossibly broad plains and peaks higher than Mt. Everest. It was as if she had handed the public a snapshot of a previously unknown world.

"Their maps projected a new world into human minds, revolutionizing geology and our understanding of the planet we live on," New York Times science writer John Noble Wilford wrote in his 2000 book "Mapmakers."

He called it "one of the most remarkable achievements in modern cartography."

The maps weren't perfect, but they were "miles ahead of second place," said Robert Fisher, a research geologist at Scripps Institution of Oceanography in La Jolla and a contemporary of Tharp. "People around the world thought that if you drained the water, the seafloor would look like her maps."

Mapping the vast, hidden seafloor was "a once-in-the-history-of-the-world opportunity" for anyone, but especially for a woman in the 1940s, Tharp recalled decades later. She had been recruited to study geology at the University of Michigan only because so many men were in the military during World War II.

"You cannot overestimate the significance of her contributions. She wasn't just a mapmaker; there was a tremendous amount of insight and scientific intuition," said Mike Purdy, director of Lamont-Doherty Earth Observatory.

Because women weren't allowed to sail on research ships in the 1940s and '50s, Tharp remained behind, painstakingly plotting sonar readings of the ocean floor often sent back by Heezen, a marine geologist with whom she spent three decades in a personal and professional partnership.

Over five years, as she pieced together a puzzle of the North Atlantic Ocean, an enormous mountain range with a puzzling peculiarity took shape. What became known as the Mid-Atlantic Ridge showed signs of a crack down the middle that led Tharp to conclude that the seafloor was spreading, a radical notion at the time.

When she told Heezen, he initially dismissed her interpretation as "girl talk" and refused to believe it for a year.

As they pieced together later maps, Heezen and Tharp helped establish the existence of a massive underwater ridge that girdles the globe, with the telltale crevice running down the center.

Her early observations and maps encouraged scientists to reexamine the theory of continental drift: the belief that the continents once had been one giant land mass that was slowly pulled apart through the movement of tectonic plates.

"She is one of the unsung heroes of the seafloor spreading-plate tectonics revolution," Purdy said.

Many remaining skeptics were convinced by a Jacques Cousteau film shown in 1959. The French explorer had attached a movie camera to a sled and had it towed across the undersea valley, returning with footage of big, black cliffs in blue water.

By the late 1960s, the theory of plate tectonics was on its way to near-universal acceptance, bolstered by seismic data that showed many earthquakes had occurred along the rift that Tharp had first illuminated with India ink and a ruler.

Tharp and Heezen's work expanded to include the South Atlantic, Indian, Arctic, Antarctic and Pacific oceans. It culminated with the map of the world's oceans, published weeks after Heezen died of a heart attack on a research expedition in 1977.

"We were upsetting all the theories," Tharp told the Associated Press in 1999. "We learned about 10 things in college, and we had disproved them all."

Tharp was born July 30, 1920, in Ypsilanti, Mich., into a mapmaking family. Her father, William, was a surveyor who made soil classification maps for the U.S. Department of Agriculture; her mother, Bertha, taught German and Latin. Tharp later calculated that she had attended two dozen schools because the family traveled for her father's work.

Following her father's advice to find something to do that she loved, Tharp piled up college degrees like points on a compass: a bachelor's in English and music, with four minors, from Ohio University in 1943; a master's in geology from the University of Michigan; and a degree in mathematics from the University of Tulsa while working as a geologist for an Oklahoma oil company.

Still searching for a challenge, she moved to New York in 1948 and joined Columbia's geology department as a research assistant. Heezen arrived two weeks later.

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