Meteoritic substances

Meteorites are of two kinds stony meteorites that are rock-like in character, and metallic meteorites that consist of metallic elements. The kinds of substances in the stony meteorites are very much like the substances in the crust of the earth, if we allow for the fact that the meteors could not bring gases or liquids with them. We feel that the other type, the metallic meteors, give valuable clues about the nature of the earth s central core. Experts have long believed that these meteorites are fragments from exploded planets that, perhaps, resembled the earth. 

Until the 1980s, yields of nucleobases obtained in prebiotic syntheses were very small. Thus, some scientists assumed that in earlier phases of molecular evolution, the nucleic acids used other bases in their information-transmitting substances. Piccirilli et al. (1990) suggested isocytosine and diaminopyridine, while Wachtershauser (1988) suggested that the first genetic material possibly consisted only of purines. However, pyrimidine (about a fifth of the total amount of purines present) had been detected in the Murchison meteorite, so that an effective pyrimidine synthesis should have been possible. 

The purine base guanine is also formed in concentrated solutions of ammonium cyanide, i.e., the same substance which became known from Or6 s adenine synthesis. Or6, as well as Stanley Miller, was involved in a new series of experiments (Levi et al., 1999). The yield of guanine is, however, 10 10 times lower than that of adenine surprisingly, the synthesis is just as effective at 253 K as at 353 K. Low temperatures seem conceivable in certain parts of Earth as well as on the Jovian moon Europa (see Sect. 3.1.5) or in the Murchison meteorite. 

Urey HC (1947) The thermodynamic properties of isotopic substances. J Chem Soc 562-581 Urey HC, Greiff LJ (1935) Isotopic exchange equilibria. J Am Chem Soc 57 321-327 Van Schmus WR, Wook JA( 1967) A chemical petrologic classification for the chondritic meteorites. Geochim Cosmochim Acta 31 747-765... 

Solution databases now exist for a niunber of the major metallic alloy systems such as steels, Ni- based superalloys and other alloy systems, and highly accurate calculation have been made which even a few years ago would have been considered impossible. The number of substance databases are increasing and the numbers of substances they include is reaching well into the thousands. Substance and solution databases are increasingly being combined to predict complex reactions such as in gas evolution in cast-irons and for oxidation reactions, and it is already possible to consider calculations of extreme complexity such as the reactions which may occur in the burning of coal in a industrial power generator or the distribution of elements in meteorites. 

The presence of organic molecules in samples of extraterrestrial matter has been known for more than a century. Some of the greatest chemists of the nineteenth century were involved in the analysis of samples of meteoritic material. They were able to show that carbonaceous chondrites (as they are now named) contain organic molecules. The first to detect carbon in a meteoritic sample was Thenard, in 1806, by analysis of a sample of the Alais meteorite. This result was confirmed in 1834 by Berzelius, who was also the first to detect the presence of water of crystallisation. Working on a sample of the Kaba meteorite, Wohler (1858) confirmed the presence of organic matter, and in a paper dated 1859 said, I am still convinced that besides free carbon this meteorite contains a low-melting point, carbon containing substance which seems to be similar to certain fossil hydrocarbon-like substances... . 

Th fall of the Orgueil meteorite in 1864 enabled various scientists to confirm the previous observations once again. Cloez noted in 1864 the remarkable similarity between the elementary composition of the terrestrial humic substances and that of the carbonaceous matter in the Orgueil meteorite . 

Amino acids - and more generally organic substances - are mainly detected in carbonaceous chondrites, a minor, carbon-rich class of meteorites. These are believed to have originated from parent bodies having underwent alteration by liquid water at some stages of their existence, as attested by geochemical studies [63]. 

Some chemical fragments of DNA and RNA can also be found in meteorites (Tables 5.1 and 5.2). For example, some meteorites have been reported to contain small amounts of adenine, one of the nucleobases found in RNA and DNA. The current view is that the Murchison meteorite contained adenine, guanine, their hydrolysis products hypoxanthine and xanthine, and uracil. The reported concentration of all those substances, however, is low, about 1.3 ppm. The Murchison and other meteorites may also contain ribitol and ribonic acid, the reduced and oxidized forms of ribose, respectively, but ribose itself has not been found.6... 

Yang J. and Anders E. (1982) Sorption of noble gases by solids, with reference to meteorites III. Sulfides, spinels, and other substances on the origin of planetary gases. Geochim. Cosmochim. Acta 46, 877—892. 

The name and symbol come from the Persian word zargun, meaning gold colored. Various forms of zirconium have been known in the form of gemstones since ancient times, but it was Klaproth who noted an unidentified substance in a jargon stone. The elemental metal (in impure form) was isolated in 1824 by Berzelius. Zirconium has been found in stars, meteorites, and lunar rocks. It exists as a compound widely in nature but is usually found in quantities too small to be of commercial interest. Zirconium is used in specialized laboratory equipment, explosives, and lamp filaments and in lotions to treat poison ivy. In the form of zirconium oxide, it is used to make gems and for specialty glass. 

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