Word: layering
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...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...
When geophysicists tag the rock strata under the ocean, they call the ocean water the first layer. On the bottom is the second layer: sediment and sedimentary rock averaging 1 km. thick. Below it lies the third layer, which seismic waves have proved to be made of unusually heavy rock. The third layer is normally unreachable, but scientists making a seismic survey in 1959 got hints that it might be exposed on the sides of the Puerto Rico Trench. In 1960 Dr. Earl Hays of Woods Hole took photographs showing fractured rock on the trench's north wall...
...climbed for 102 miles before blossoming, folded its petals only after it dropped within 65 miles of the earth's surface. When it finally landed, Physicist Robert K. Soberman of the Air Force Cambridge Research Laboratory hoped to find a few micrometeor punctures in the three-layer sandwich of thin Mylar film and Plexiglas that lined the Aerobee's dust catchers. What he actually found was something quite different: during each second of exposure, some ten meteorites had hit each square centimeter. Most of the holes were microscopic, but a few could be spotted with the naked...
...dust layer of such density has ever before been observed in space, and Dr. Soberman cannot yet explain his rocket's rich catch. One possible theory is that micrometeorites may have electric charges of the same sign-either positive or negative-when they arrive from space. The charge may accumulate near the top of the atmosphere, slow down later-arriving particles by electrostatic repulsion and make them linger there...
...second dust-catching rocket launched from Eglin Air Force Base, Fla., carried instruments that reported micrometeorite impacts and sent the information to earth by radio. The tapes of this test will not be fully interpreted for some time, but they have already roughly confirmed the existence of the dust layer. When the analysis is finished, Dr. Soberman hopes to have a better explanation of the mysterious micrometeorite belt that hangs like a faint cloud at the outer fringe of the atmosphere...