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To investigate the extraterrestrial origin of organic compounds, the 13C / 12C ratio is usually used. 21.1. Soil samples, of dimensions identical to those of the Murchison meteorite, collected around the fall site had a (A) 13C / 12C ratio equal to that of the meteorite. (B) 13C / 12C ratio lower than that of the meteorite. (C) 13C isotope greater than that of the meteorite. (D) the amount of the 13C isotope equal to that of the meteorite. 21.2. Consider the following statements, referring to different bodies in the solar system. 1. Chondrites have been studied from a petrographic and chemical point of view. 2. Asteroids are essentially made up of ice and gases. 3. Comets have concentric orbits around the Sun. (A) 3 is true; 1 and 2 are false. (B) 1 and 2 are true; 3 is false. (C) 2 and 3 are true; 1 is false. (D) 1 is true; 2 and 3 are false. 21.3. The age of the solar system can be estimated by radiometric dating (A) of the lunar rocks collected in the meteorite impact craters. (B) meteorites originating from asteroids that have undergone differentiation. (C) of chondrites, regardless of whether they contain organic compounds. (D) of the oldest rocks that make up the cratons on planet Earth. 21.4. The Moon is a satellite that presents (A) lunar seas where basic rocks predominate. (B) a dense atmosphere made up of nitrogen. (C) predominance of metamorphic rocks in the crust. (D) the surface covered by consolidated sediments. 21.5. The telluric planets are essentially _______, and the giant planets have _______ density. (A) rocky … high (B) rocky … low (C) gaseous … high (D) gaseous … low 22. In order to contribute to the assessment of the potential use of aquatic vegetation characteristic of uranium-rich areas in the bioindication of contamination of uranium and / or phytoremediation (use of plants to remove contaminants) from water contaminated with this metal, a team of researchers analyzed 71 species of aquatic plants from a vast area, corresponding to the uraniferous region of Beiras.

10. 9 The uraniferous deposits in the studied area are located in granites and in the surrounding areas. A large part of these deposits were explored, with the leaching process privileged, as the main method of processing the ore. The sampling was carried out practically in the whole area of ​​the province. The sampling points were established in water courses, in places where it was possible to observe the occurrence of aquatic species. In these places, both water samples and floating or rooted aquatic plants were taken. The entire sample included 185 sites, with 71 species identified, belonging to 41 different families. For the analysis of the uranium content, the waters were filtered and acidified. The plants were washed, first under running water and then in distilled water, to remove any soil residue or other impurities, and then dried in an oven at 60 ° C and ground for chemical analysis. Table 1 presents a summary of the analytical results of the water samples, with uranium concentrations expressed in μg / I. Table 2 presents a summary of the analytical results of the samples of the most representative plants in the studied area, with uranium concentrations expressed in mg / kg dry weight.