SP-345 Evolution of the Solar
System
FIGURE 20.6.2a.- Comparison of solar
photospheric abundance estimates with measurements on carbonaceous
meteorites of Type I. Each analytical chondrite value, normalized to
silicon, has been divided by each of the several current photospheric
values. Four of the ratio values for mercury (Z=80) exceed 20 and are
not shown in the diagram. Data compiled by L. Shawl It has commonly
been assumed that these two materials can be regarded as splits from
a chemically homogeneous body "the solar nebula" having "cosmic
abundances" of elements. Except for components with high vapor
pressures or nuclear instabilities the compositions of these
meteorites and of the solar photosphere then ought to approach
identity, and the elemental abundance ratios should be close to 1.
The strong scatter of data in the figure shows, however, that they do
not provide a basis for the assumption of a close agreement between
the solar photosphere and this group of meteorites (see also fig.
20.6.2b).
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