Meteoric abundance

Na is likely deposited in the upper atmosphere by meteors along with other metals (Clemesha et al., 1981) and distributed by solar winds (Happer et al., 1994). This atomic layer is "eaten away" at its bottom by chemical reactions (e.g. molecule and aggregate formation). Fe, Al, Ca are more abundant than Na, but the D2 transition is so strong that it provides the largest product of column density CNa and transition cross section, nominally 10 — 10" atoms/cm. The layer has been studied mostly with Lidar technique (Blamont and Donahue, 1961 Albano et al., 1970 Bowman et al., 1969 Sarrazin, 2001). 

This new edition includes results from recent space missions, including WMAP and FUSE, new material on abundances from stellar populations, nebular analysis and meteoric isotopic anomalies, and abundance analysis of X-ray gas, and several extra problems at the end of chapters. 

It has been common belief for many years that the abundance in meteoric waters carries no additional information to that of Although mass-independent fractionations are not known to occur in water, H2 0 is a useful tracer within the hydrologic cycle (Angert et al. 2004 Luz and Barkan 2007). Improvements in analytical techniques allow to measure and 5 0 with a precision of a few 0.0 l%c which permits calculation of with similar precision and the tracing of very small variations. 

Figure 8.15. Comparison of mole % CO2 in natural gas and ratio of secondary porosity to total porosity with depth for the Wilcox Formation in Texas. The shallow depth points probably have abundant secondary porosity as a result of meteoric water diagenesis, while deep secondary porosity is associated with the increase in CO2. (After Franks and Forester, 1984.)...

An alternative to the terrestrial synthesis of the nucleobases is to invoke interstellar chemistry. Martins has shown, using an analysis of the isotopic abundance of 13C, that a sample of the 4.6 billion year old Murchison meteorite which fell in Australia in 1969 contains traces of uracil and a pyrimidine derivative, xanthine. Samples of soil that surrounded the meteor when it was retrieved were also analyzed. They gave completely different results for uracil, consistent with its expected terrestrial origin, and xanthine was undetectable [48], The isotopic distributions of carbon clearly ruled out terrestrial contamination as a source of the organic compounds present in the meteorite. At 0°C and neutral pH cytosine slowly decomposes to uracil and guanine decomposes to xanthine so both compounds could be the decomposition products of DNA or RNA nucleobases. They must have either travelled with the meteorite from its extraterrestrial origin or been formed from components present in the meteorite and others encountered on its journey to Earth. Either way, delivery of nucleobases to a prebiotic Earth could plausibly have been undertaken by meteors. The conditions that formed the bases need not have been those of an early Earth at all but of a far more hostile environment elsewhere in the Solar System. That environment may have been conducive to the production of individual bases but they may never have been able to form stable DNA or RNA polymers this development may have required the less extreme conditions prevalent on Earth. 

As meteoric material is evaporated, a number of high energy gas-phase collision processes occur. These processes, examples of which are listed in Fig. 1, involve both collisions between neutrals and neutrals and ions. Metal atoms, Me, are abundant in all meteoric bodies, and play an important role for several reasons (i) Metal atoms and ions frequently have low lying excited states with high oscillator strengths and are, therefore, easily identified and traceable (ii) Metal atoms have low ionization potentials and can be ionized fairly efficiently in high velocity neutral collisions (iii) Atomic metal ions have very long lifetimes with respect to ion-molecule reactions and electron-ion recombination compared with molecular ions, which rapidly dissociatively recombine with electrons. 

Many attempts have been made to obtain spectra of meteor trails. Probably the best spectra ever obtained were by Millman and his colleagues at the Dominion Observatory. Figures 4 and 5 are a comparison of spectra stemming from a slow (probably Giacobinid) and a fast (Perseid) meteor, respectively. The spectrum of the low velocity meteor exhibits neutral emission lines of Mg, Fe, and Ca, the most abundant metals in most meteoroids. The strong Na D lines as well as a hint at excited N2 are also visible. By contrast, the spectrum of the high velocity meteor shows very... 

Due to the high abundance of Fe in all meteoroids, a large number of Fe lines are observed in all meteor spectra. Molecular metal oxide spectra for FeO, CaO, AlO, and MgO have also been identified. Other observed molecules include N2, CN and C2- Millman and coworkers have tentatively reported the observation of O2+ and N2 emissions. 

There is abundant evidence from cometary meteors and tidal breakup, suggesting that comets are very weakly consolidated materials (Weissman, 1986). Sekanina (1982) found that... 

Precise measurements of the natural abundance of deuterium and in meteoric waters started shortly after World War II and the interest of such measurements for studying various aspects... 

Anders E. and Grevesse N. (1989) Abundances of the elements meteoric and solar. Geochim. Cosmochim. Acta 53, 197-214. 

It is clear that the relative importance of pressure solution as a mechanism of IGV decline increases markedly with depth. It also varies in importance among units of different bulk composition. For example, pressure solution appears to be widespread in sandstones of plutonic derivation (Thomas et al, 1993 Oelkers et al, 1996 Spotl et al, 2000), but not in the largely volcanogenic Cenozoic sandstones of the Gulf of Mexico basin (Land et al, 1987 Land and Milliken, 2000). Controls that appear to favor the development of pressure solution include abundant potassium-rich micaceous debris, a history of meteoric water incursion, and elevated temperature (>100 °C ). 

Fig. 2. West to east cross-section across San Joaquin basin. See Fig. 1 for location of the cross-section line. Most of basin-fill is marine, including the Stevens sandstone, and is at maximum burial depth. Non-marine strata are Chanac and Kem River Formations. Low lateral continuity of beds and abundant shales have prevented meteoric water from entering the deep central basin. Cross-section from California Division of Oil and Gas.

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