Extraterrestrial samples

Percentage of meteorites seen to fall. Chondrites. Over 90% of meteorites that are observed to fall out of the sky are classified as chondrites, samples that are distinguished from terrestrial rocks in many ways (3). One of the most fundamental is age. Like most meteorites, chondrites have formation ages close to 4.55 Gyr. Elemental composition is also a property that distinguishes chondrites from all other terrestrial and extraterrestrial samples. Chondrites basically have undifferentiated elemental compositions for most nonvolatile elements and match solar abundances except for moderately volatile elements. The most compositionaHy primitive chondrites are members of the type 1 carbonaceous (Cl) class. The analyses of the small number of existing samples of this rare class most closely match estimates of solar compositions (5) and in fact are primary source solar or cosmic abundances data for the elements that cannot be accurately determined by analysis of lines in the solar spectmm (Table 2). Table 2. Solar System Abundances of the Elements ... 

The scheme given in Fig. 2.1 represents normal analytical procedures in off-line analysis. It contains all the steps that must be considered in principle. However, there could be reasons to reduce the course of action. Not in all cases is the analyst able to take samples by himself or check the sampling procedure. Sometimes he or she must accept a situation in which he or she has to receive a given sample (e.g., in extreme cases, extraterrestrial samples, autopsy matter). 

Three Isotope Plots of Terrestrial and Extraterrestrial Samples... 

Abstract The theoretical framework needed for interpretation of kinetic isotope effects on unimolecular reactions is reviewed. Application to the satisfactory rationalization of the theoretically puzzling mass independent isotope effect observed for oxygen isotope fractionation in extraterrestrial samples is described. 

Figure 6. Summary of ranges in isotopic compositions for natural terrestrial samples as discussed in this volume. Isotopic variability in extraterrestrial samples is often greater. Isotopic compositions reported as 5 values in units of per mil (%o), based on isotopic ratios and reference standards as used in this volume (Table 1). Note that the range of isotopic compositions for Li is much greater than the scale used in the diagram, where 5 Li values vary from -21 to +54. In many cases, relatively large isotopic fractionations occur during redox reactions (see Chapter 3), and the common oxidation states in near-surface natural environments are listed on the left.

Figure 2. Magnesium three-isotope plot showing terrestrial and extraterrestrial samples relative to the predicted equilibrium and kinetic mass fractionation laws. The slopes in the caption refer to the P values that characterize the mass fractionation laws.

Meteorites (Fig. 1.4) are central to cosmochemistry, because they are our most accessible source of extraterrestrial samples. Though people have seen stones falling from the sky for... 

The following minerals are important in meteorites and other extraterrestrial samples. Some important classes of minerals in terrestrial rocks are not observed or are extremely rare in meteorites or planetary samples (e.g. micas, amphiboles) and will not be considered. 

The Re- Os method was first applied to extraterrestrial samples in the early 1960s when Hirt et al. (1963) reported a whole-rock isochron for 14 iron meteorites that gave an age of 4 Ga. Further development of this system was hindered by several technical difficulties. Rhenium and osmium each exist in multiple oxidation states and can form a variety of chemical species, so complete digestion of the samples, which is required to chemically separate rhenium and osmium for mass spectrometry, is difficult. In addition, accurate determination of rhenium abundance and osmium isotopic composition requires spiking the samples with isotopically labeled rhenium and osmium, and equilibration of spikes and samples is challenging. A third problem is that osmium and, particularly, rhenium are very difficult to ionize as positive ions for mass spectrometry. These problems were only gradually overcome. 

Another area of significant effort has been to determine the decay constant for 176Lu. The half-life has not been precisely measured in the laboratory recent determinations range from 3.69 x 1010 years to 4.08 x 1010 years (e.g. Grinyeret al., 2003). The preferred value (t1/2 =3.73 x 10 years) is derived from measurements of terrestrial and extraterrestrial samples with known ages determined by U-Th-Pb chronology. 

Chiral separation of FITC-labeled amino acid enantiomers was performed on a glass chip using fluorescent detection. Analysis time ranged from 75 s for the most basic amino acids to 160 s for the most acidic ones. y-CD was used as the chiral selector [627]. Chiral separation of amino acids in extraterrestrial samples or meteorites were also performed [610,628],... 

The rate of cosmogenic production of Al is still lower than that of Be, and in fresh sediments the ratio A1 A1 is of the order of 10 ", whereas the ratio Be Be is of the order of 10. This makes the determination of A1 in terrestrial samples very difficult. On the other hand, the production rate of A1 in meteorites and samples from the surface of the moon is comparable with that of Be, because in these samples low-energy protons from the sun contribute appreciably to the production of Al. Measurement of the A1 Be ratio in extraterrestrial samples provides information about their history. 

Swart P. K., Grady M. M., and Pillinger C. T. (1983) A method for the identification and elimination of contamination during carbon isotopic analyses of extraterrestrial samples. Meteoritics 18, 137-154. 

Detection of biomass is an important application of analytical pyrolysis and it includes several topics. One such topic is the measurement of microbial biomass in attempts to substitute for traditional microbiological methods. Another topic is the detection of specific biomarkers for geochemical logging purposes. Pyrolytic studies were also useful in organic marine geochemistry [72]. An interesting application of biomass detection is the search for life in extraterrestrial samples. 

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