American Treasures of the Library of Congress: Reason

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Mapping the Ocean Floor

"Contours, 0504N" for Atlantic Ocean Floor.
T. Casper
"Contours, 0504N" for Atlantic Ocean Floor.
Colored pencil on mylar and
graphite on paper, July 1973
Geography & Map Division
Gift of Marie Tharp, 1995-96 (118.1)

For 30 years, oceanographic cartographer Marie Tharp and marine geologist Bruce Heezen compiled the first comprehensive physiographic diagram of the ocean floor. Using such data as continuous echograms and closely spaced depth soundings, they constructed preliminary contour diagrams, such as the one for this area in the North Atlantic. These diagrams demonstrated that the sea floor was not a monotonous "abyssal plain," as many had previously thought, and that mid-ocean ridges paralleled the shapes of the continents, thus setting the stage for the acceptance of the theory of plate tectonics.

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