Tektites vs. terrestrial rocks: a comparison of variance in compositions

Mathematics – Probability

Scientific paper

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Scientific paper

Tektites are much more similar chemically to certain terrestrial rocks than to known meteorites; this fact supports the possibility that tektites have been formed by the melting and quenching of terrestrial rocks by impact of comets or meteorites or by lightning. This paper presents the results of an attempt to estimate the probability of such occurrences by analysis of the variation in chemical compositions in tektites and igneous and sedimentary rocks. Sixty chemical analyses each of igneous and sedimentary rocks with a range of SiO 2 content equal to that of analysed tektites were picked at random from the literature, subject to restrictions on quality and area. The variance, for each major oxide, of the rock compositions was compared to the corresponding variances for sixty-six analysed tektites by the variance ratio test, and was found to be significantly greater for both rock classes than the tektite variance. All basic assumptions, including representativeness of sample analyses, effect of analytical error on between-sample variance, and compositional changes due to fusion were justified. This study suggests that tektite formation by random occurrences such as cometary impact must do two things to account for tektite compositions: terrestrial rocks of fairly restricted composition must be selected for fusion, and the variance in composition within this selected sample must be suppressed. The probability that random processes will do both is shown to be considerably less than 0.001. The following conclusions were reached: 1. (1) Tektites are a distinct geochemical class characterized by restricted chemical composition and functional variation of major oxides with silica content. 2. (2) Tektites have not been formed from terrestrial materials by any natural process thus far suggested. 3. (3) Tektite formation involved some sort of systematic chemical differentiation. These conclusions point to an extra-terrestrial origin for tektites.

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