Like many other women scientists of her day, Tharp found an unexpected opportunity in the form of a world war. But given the scant number of women in geology at the time-women obtained fewer than 4 percent of all earth sciences doctorates between 19-it’s surprising that Tharp was able to pursue her passion. Department of Agriculture would inherit a taste for both geology and cartography. In retrospect, it makes plenty of sense that the daughter of a soil surveyor for the U.S. Tharp, who was born in 1920, came of age during a time that was suspicious of women who chose to make science their life’s work. But Tharp’s discovery of the 10,000-mile-long Mid-Atlantic Ridge*-a find that showed that the sea floor was spreading-was initially dismissed as “girl talk.” But what about the way we think about what’s underneath? That was the case in 1953, when a young geologist named Marie Tharp made a map that vindicated the controversial theory of plate tectonics. By funding expeditions to spreading centers in the Atlantic and the Pacific, NOAA Ocean Exploration is helping scientists to draw connections between volcanic, tectonic, hydrothermal, and biological systems in order to better understand the Earth’s remarkable, evolving geography.There’s no denying that maps can change the way we think about the world. Due to the fast spreading rates, there is no rift valley in the Pacific, just a smooth volcanic summit with a crack along the crest that is much smaller than the Atlantic rift valley.ĭespite being such a prominent feature on our planet, much of the mid-ocean ridge system remains a mystery. In contrast, the East Pacific Rise is spreading quickly, at rates of 6 to 16 centimeters (3 to 6 inches) per year. The Mid-Atlantic Ridge runs down the center of the Atlantic Ocean, slowly spreading at a rate of 2 to 5 centimeters (0.8 to 2 inches) per year and forming a rift valley that is about the depth and width of the Grand Canyon. Two well-studied mid-ocean ridges within the global system are the Mid-Atlantic Ridge and the East Pacific Rise. The speed of spreading affects the shape of a ridge – slower spreading rates result in steep, irregular topography while faster spreading rates produce much wider profiles and more gentle slopes. As the plates separate, molten rock rises to the seafloor, producing enormous volcanic eruptions of basalt. Mid-ocean ridges occur along divergent plate boundaries, where new ocean floor is created as the Earth’s tectonic plates spread apart. The majority of the system is underwater, with an average water depth to the top of the ridge of 2,500 meters (8,200 feet). The massive mid-ocean ridge system is a continuous range of underwater volcanoes that wraps around the globe like seams on a baseball, stretching nearly 65,000 kilometers (40,390 miles). This system forms the longest and largest mountain range on Earth, winding its way between the continents. New ocean crust, shown in this map in red, forms along the divergent plate boundaries of the ridge system. The nearly continuous, global mid-ocean ridge system snakes across the Earth’s surface like the seams on a baseball.
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