Comparing the two maps, Heezen and Tharp realized that the earthquake epicenters fell inside the rift valley. When she did, the rift valley was still there.Īnother research assistant was plotting locations of earthquake epicenters on a map of the same size and scale. Heezen called this idea “girl talk” and told Tharp to recalculate and redraft. Tharp suggested that it was a rift valley – a type of long trough that was known to exist on land. Tharp’s careful plotting of six east-to-west profiles across the North Atlantic revealed something no one had ever described before: a cleft in the center of the ocean, miles wide and hundreds of feet deep. These views made it easier to visualize the ocean floor’s topography and create a physiographic map. One of her important innovations was creating sketches depicting what the seafloor would look like. Next she’d read the depth at each location off the sonar profile, mark it on the ship’s track and create her own condensed profile, showing the depth to the ocean floor versus the distance the ship had traveled. Then she’d carefully mark where the ship had traveled. Starting with a large blank sheet of paper, Tharp marked lines of latitude and longitude. (c) sketches features shown on the profiles. (b) plots depth recordings as profiles, exaggerating their height to make features easier to visualize. (a) shows the position of two ship tracks (A, B) moving across the surface. These are long paper rolls that show the depth of the seafloor along a linear path, measured from a ship using sonar.Īn illustration of Marie Tharp’s mapping process. Tharp worked with Bruce Heezen, a grad student who gave her seafloor profiles to draft. Women couldn’t go on research ships, but Tharp could draft, and was hired to assist male graduate students. “Girls were needed to fill the jobs left open because the guys were off fighting,” Tharp later recalled.Īfter working for an oil company in Oklahoma, Tharp sought a geology job at Columbia University in 1948. But then in 1943 she enrolled in a University of Michigan master’s degree program designed to train women to be petroleum geologists during World War II. Mapping the unseenīorn in Ypsilanti, Michigan, Tharp studied English and music in college. The total walk would be about 3,800 miles (6,000 kilometers) – almost twice the length of the Appalachian Trail. Then back down to the ocean floor, until I began trekking up the European continental slope to Lisbon. Then I’d start a slow climb up the Mid-Atlantic Ridge, a submerged north-south mountain range.Īfter ascending to 8,200 feet (2,500 meters) below sea level to the ridge’s peak, I would descend several hundred feet, cross the ridge’s central rift valley and proceed up over the ridge’s eastern edge. I’d need to detour around underwater mountains, called seamounts. Then downward towards the Sohm Abyssal Plain. The journey would take me out along the continental shelf. Thanks to Tharp’s hand-drawn renditions of the ocean floor, I can imagine a walk across the Atlantic Ocean bottom from New York City to Lisbon. Tharp’s East-West profiles across the North Atlantic.
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