Word: layered
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Dates: during 1960-1969
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...plentiful in the byproducts of plutonium manufacture, and the AEC's Oak Ridge National Laboratory, taking careful precautions, decided to use it. It was converted into strontium titanate, which is chemically inert and virtually insoluble, then formed into eleven pellets and welded into a three-layer jacket. All this had to be done by remote control from behind thick radiation shields-or the operators would not have lived to do more work...
...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...
...they had been exposed to the iron and manganese oxides that slowly deposit from sea water. Other surfaces were fresh and light green. Dr. John B. Hersey, chief scientist of the cruise, believes that the chunks with fresh faces were broken by the dredge out of the mysterious third layer. If so, they may show what the crust of the earth was like billions of years ago, before the infant ocean rained sediment...
...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...