Marie Tharp, 1920–2006, American oceanographer and cartographer, grad. Univ. of Michigan (M.A. 1944). A geologist with experience in mapping, she came to Columbia Univ. as a geology research assistant in 1948, retiring in 1983. Painstakingly converting oceanographic soundings to physiographic maps of the North Atlantic Ocean floor, Tharp, working with Bruce Heezen, identified (1952) the Mid-Atlantic ridge and rift valley; when Heezen's group confirmed that seismic activity along the ridge was centered on the rift, it provided solid evidence of seafloor spreading and plate tectonics. Tharp and Heezen's work mapping the oceans ultimately led to the discovery of a 40,000 mi (64,000 km) panoceanic underwater ridge, made visible in their World Ocean Floor map published (1977) by the Office of Naval Research.
See biography by H. Felt (2012).