Elemental and Isotopic Abundances

The existence and distribution of the chemical elements and their isotopes is a consequence of nuclear processes that have taken place in the past in the Big Bang and subsequently in stars and in the interstellar medium (ISM) where they are still ongoing. These processes are studied theoretically, experimentally and obser-vationally. Theories of cosmology, stellar evolution and interstellar processes are involved, as are laboratory investigations of nuclear and particle physics, cosmo-chemical studies of elemental and isotopic abundances in the Earth and meteorites and astronomical observations of the physical nature and chemical composition of stars, galaxies and the interstellar medium. 

Almost all of the elements heavier than He are synthesized in the interiors of stars. The work of Burbidge et al. (1957) gives the theoretical framework for the synthesis of the elements. The experimental evidence of active nucleosynthesis came from the discovery of the unstable nuclei of technetium in the spectra of red giants (Merrill 1952). The solar elemental and isotopic abundances which are taken from the primitive carbonaceous chondrites constitute the guidelines for testing such models (Anders and Grevesse 1989). A minimum of eight basic processes are required to reproduce the observed compositions. Nucleosynthetic... 

Murthy VR (1962) Isotopic anomalies of molybdenum in some iron meteorites. J Geophys Res 67 905-907 Murthy VR. 1963. Elemental and isotopic abundances of molybdenum in some meteorites. Geochim. Cosmochim. Acta 27 1171-1178... 

List five techniques by which elemental and isotopic abundances can be measured. 

In recent decades, spectroscopy has revealed that the elemental and isotopic abundances in the galaxy vary with radial position and that the Sun has a somewhat different composition than the molecular clouds and diffuse interstellar medium in the solar neighborhood. For this reason, we can no longer think of the solar system abundances as truly cosmic abundances. 

Element and isotopic abundances of Si and Mg in CAIs suggest evaporation, (a) Correlated isotopic fractionations in Type CAIs. (b) Si02 versus MgO for CAIs, relative to the calculated condensation sequence abundances (heavy line). Unmelted Type A inclusions (open circles) follow the condensation path, whereas partly melted Type inclusions (filled circles) deviate, because of loss of both Mg and Si, as illustrated by the arrow. Modified from Davis and Richter (2004). 

Our general understanding of how the solar system came to be comes from a variety of different sources. Astronomical observations and theoretical modeling provide a broad picture of how stars form. Elemental and isotopic abundances in the solar system,... 

For a given astrophysical scenario for the s- or r- process, the corresponding elemental and isotopic abundances can be reliably computed only if the relevant nuclear (and, in some cases, atomic) physics input data are available. In return, careful studies of required nuclear properties and comparisons of the calculated and observed abundances often give a hint as to the astrophysical conditions appropriate for the s- or r- process site (see [MAT85a] for a review). 

In contrast, the study of stellar grains permits information to be obtained about individual stars, complementing astronomical observations of elemental and isotopic abundances in stars (e.g., Lambert, 1991), by extending measurements to elements that cannot be measured astronomically. In addition to nucleosynthesis and stellar evolution, presolar grains provide information about galactic chemical evolution, physical properties in stellar atmospheres, mixing of SN ejecta and conditions in the parent bodies of the meteorites in which the grains are found. 

Students can use this tool to explore the variety of elements and isotopes, understand the idea of abundances and mass fractions, compare elemental and isotopic abundances (for example, how much gold is there compared to iron or how much there is compared to 0), and appreciate the different number of nucleosynthetic processes that have built up the Solar System s supply of isotopes. In a soon to be released update of the tool, users will also be able to convert between the various abundance notations used throughout the scientific literature such as the cosmochemical and logarithmic notations, fractional... 

Jupiter and other giant planets Mass spectrometry (Galileo probe) In-situ interferometry (Galileo probe) Radio occultation infrared spectroscopy (Voyager) He-Ar, Xe elemental and isotopic abundance in outer Jovian atmosphere. Mahaffy et al. 2000. He abundance in outer Jovian atmosphere, v. Zahn et al. 1998. He abundance in giant planet outer atmospheres. Comath et al. 1991 Comath and Gautier 2000. 

Table 7. Elemental and isotopic abundances of noble gases (+H, C, and N) in Jupiter.

Despite the noted ambiguities, several important comparisons between noble gas element and isotope abundances in the atmospheres of Venus and the Earth are possible (Table 8), which are discussed in more detail by Pepin and Porcelli (2002, this volume) ... 

The rest of this review is organized as follows. First a general overview is given of elemental and isotopic abundance patterns of major and/or well-defined components. This is followed by a chapter that gives a discussion of origin and history of these components and that also discusses some less common and/or less well-characterized components. After possible relationships are considered, a short summary is given. 

Chemical element and isotope abundances. The abundance of chemical elements in the solar system (see Fig. 12.13 in Chap. 12, Vol. 2), as well as in Earth s crust and seas usually shows maximum values at magic proton and/or neutron numbers (Firestone et al. 1996). The number of stable isotopes and isotones is remarkably high for magic numbers of Z and N (see O Fig. 2.7). 

Mass spectrometry is ideally suited to the investigation of planetary atmospheres and cometary material in terms of both elemental and isotopic abundances. Mass spectrometers have been an integral component of space probe instrumentation because they are mechanically robust, have a low power consumption, yet are sensitive and versatile. 

Basalts, basaltic andesites, and andesites with this distribution are common in some island arcs (e.g., Jakes and Gill, 1970 Ewart et al., 1973 Taylor et al., 1969). Their presence is believed to result from melting of subducted oceanic crust. By and large, the sediment layers which lie above the ocean floor tholeiites and are derived mainly from continental material are not subducted but piled up against continental margins in some manner that prevents their modifying significantly the trace element and isotopic abundances of oceanic crustal matter in the production of this class of island arc volcanics. Nor does ocean water severely modify the lanthanide distributions in volcanics that are extruded under... 

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