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Iridium and osmium concentrations were measured in dated deep-sea sediments by neutron activation analysis to attempt to set limits on the influx rate of cosmic matter. Twentyone measurements on five cores from the central Pacific gave Ir and Os contents from 0·06 to 0·4 ppb, with an observed precision of ±15 percent. The Ir and Os contents were correlated with each other: Ir = (1·2 ± 0·2)Os. Both tended to increase with decreasing sedimentation rate. The Ir content can be represented by the expression: Ir (ppb) = (0·07 ± 0·08) + (0·094 ± 0·047)1/rs where rs is the sedimentation rate in mm per 1000 years from Th230Th232 ratios. If the first term is interpreted as an average terrestrial component and the second term, as an exclusively cosmic component which is diluted in proportion to the sedimentation rate, an upper limit to the influx rate of cosmic matter may be established on the basis of the average Ir content of some representative meteoritic material. With an assumed Ir content of 0·42 ppm, the value in Type I carbonaceous chondrites, the influx rate for the entire earth becomes (6 ± 3) × 104 tons/yr. This value represents an average over the last 105 to 106 years; the mass range effectively sampled by this method is ~10−14 to ~1012 g. A firm upper limit on the influx rate can be obtained by assuming that all the Ir and Os in deep-sea sediments is of cosmic origin. The value obtained is between 0.5 × 105 and 1.5 × 105 tons/yr. It is more than an order of magnitude lower than other estimates based on the Ni content of deep-sea sediments or particles counts by satellites.

A sample of the Pesyanoe meteorite has been examined by X-ray diffraction microtechnique, in an effort to find minerals of known gas-trapping tendency and thus explain the high helium content of the meteorite. Determinations of enstatite, feldspar, and troilite by earlier workers have been confirmed. The existence of many variant minor pyroxene phases, including clinopyroxene and rhombic pyroxene with stacking faults, shows that the history of the meteorite must have involved several complex heating and cooling cycles. In addition, there exists a variety of Sulfides, which includes not only both magnetic and non-magnetic troilites, daubreelite, and oldhamite, but also a new mineral, MgS, the composition of which has been checked by spectrographic analysis. All the sulfides present show a high degree of crystal imperfection. Vaterite (μ-CaCO3) has been found, but it is not known whether it is of terrestrial or antecedent origin. The high concentration of dislocations in the sulfides indicates a comparable abundance of other lattice defects. It is suggested that lattice defects of various kinds are the most probable loci of the gas atoms. The gases apparently entered the sulfide crystals during their growth, either in a closed magma chamber or in a hot gas stream containing both noble gases and sulfur compounds. Some circumstantial evidence favours the latter alternative.