The most accessible part of the earth's interior is at the ocean's bottom, where the crust is thin. Project Mohole, the U.S. attempt to reach the boundary layer between the earth's crust and mantle by drilling off the coast of Mexico, so far has penetrated only ordinary, surface-type rocks. Last week, the Woods Hole Oceanographic Institution reported far better success with another method. From the fractured north wall of the Puerto Rico Trench, its research ship Chain has dredged up the first samples of "third layer" rock ever gathered by man.
When geophysicists...
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