4241LNOT02_S11_PP

4241LNOT02_S11_PP - Environmental Geochemistry, GLY...

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Environmental Geochemistry, GLY 4241/5243, © David Warburton, 2011 1 LECTURE 2 - ELEMENTAL DISTRIBUTIONS IN THE UNIVERSE AND THE SOLID EARTH Note: Slide numbers refer to the PowerPoint presentation which accompanies the lecture. Element Distributions, slide 1 here INTRODUCTION In Lecture 1 we found that an aim of geochemistry, as defined by Goldschmidt, was the study of the distribution and amounts of the chemical elements in minerals, ores, rocks, soil, water, and the atmosphere. A study of this information will provide a background for all environmental geochemical studies involving elements. Element Distributions, slide 2 here Elemental abundances may be expressed in several ways. One is on a number of atoms basis. This assumes that we have, say, one million atoms. Of these one million atoms, so many atoms will be oxygen, so many will be silicon, etc. This is purely a numerical counting system. Another method allows for the weight of each atom. Figures will be reported in weight percent or weight per million grams. If we have a million gram sample, so many grams are oxygen, so many are silicon, etc. This method increases the numbers for heavy elements, while decreasing the numbers for lighter elements. Another method is based on volume. Large atoms (anions and large cations) take up much more volume than small atoms. Another method is used in discussing "cosmic" abundances. The cosmic abundance figures are an attempt to estimate the elemental composition of the entire universe from data gathered by earth-based astronomical and satellite data. They are generally reported relative to the
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Environmental Geochemistry, GLY 4241/5243, © David Warburton, 2011 2 abundance of silicon. Data for all elements are converted to their abundance relative to 1,000,000 atoms of silicon. Although cosmic abundances are not usually useful to an environmental scientist, examining the figures to see just how different the earth really is from the average abundances seen in the universe is useful. COSMIC ABUNDANCES The cosmic abundance values (Mason and Moore, 1982) are shown in table 2-1. Several features of this table immediately stand out. Element Distributions, slide 3 here (these are solar abundacnes) 1. The light elements are much more abundant than the heavy elements.
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4241LNOT02_S11_PP - Environmental Geochemistry, GLY...

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