. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. SECT. 3] PELAGIC SEDIMENTS 675 studied the metallic spherules and have investigated the nature of the silicate chondrules. The size distributions both of the nickel-iron spherules and of the olivine-pyroxene chondrules found on the deep ocean floor (Fig. 12) are in remarkable disagreement with the tentative size distribution of micrometeorites derived by impact, counting from the satellites 1958 Alpha and 1959 Eta (LaGow and Alexander, ojp. cit.). An exponential increase in number of particles with decreasing size below 10
. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. SECT. 3] PELAGIC SEDIMENTS 675 studied the metallic spherules and have investigated the nature of the silicate chondrules. The size distributions both of the nickel-iron spherules and of the olivine-pyroxene chondrules found on the deep ocean floor (Fig. 12) are in remarkable disagreement with the tentative size distribution of micrometeorites derived by impact, counting from the satellites 1958 Alpha and 1959 Eta (LaGow and Alexander, ojp. cit.). An exponential increase in number of particles with decreasing size below 10-20 [j. is indicated by the satellite observations, although cosmic particles from the ocean floor show a marked decrease in No. of spherules in deep sea sediment 40 30 20 IO- C-. No of satellite impacts of micrometeorites per m^sec 10' 10" 5 10 20 40 10- Fig. 12. Size distribution of cosmic spherules from pelagic sediments, and from micro- meteorites in oviter space. Shaded histogram = iron spherules; Ime-boiuided histogram = silicate spherules from pelagic sediments (data from Hunter and Parkin, 1960); filled circles = impact observations from satellites 1958 Alpha and 1959 Eta (computed from data in LaGow and Alexander, 1960, assuming an average particle density of ). frequency below 25 y. and a comparatively large number of big (90 to 300 [i) silicate chondrules. This corroborates the idea that the cosmic material found on the ocean floor represents debris of meteorites, as suggested by Fredriksson (1959), rather than the original cosmic dust. Large numbers of magnetic spherules of unknown origin and composition, ranging in size from less than a micron to several microns, are frequently observed in sediments (see, for example, Crozier, 1960). Analyses of such bodies indicate a heterogeneous origin. Many of the magnetic spherules previously assumed to have been derived from outer space have been shown by Fredriks- son (1961) to consist of volcanic glass with inclusio
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