Today is the 77th birthday of Marie Tharp, an oceanographic cartographer whose maps of the world's sea floors helped shape a new view of Earth--plate tectonics--in which crustal plates constantly shift and move on top of the mantle. During the 1940s Tharp and her co-worker Bruce Heezen used sonar to gather data on the topography of the floor of the Atlantic Ocean. From this they assembled in 1952 the first three-dimensional picture of the sea floor, which revealed a deep valley along the crest of the Mid-Atlantic Ridge. They suggested that this was a plausible location where molten rock wells up to form new oceanic crust. By 1959 their interpretation was validated by data showing high seismic activity in the suspected rift valley.
[Source: Emily McMurray, Ed., Notable Twentieth Century Scientists (Gale Research Inc., ITP, 1995).]