Solar system abundances of the isotopes

Why can one assume that the isotopic compositions of elements on the Earth are representative of the bulk solar system This was not obvious in the beginning. Isotope-ratio measurements of meteorites made in the late 1950s appeared to show significant variations. However, within a few years, it was shown that those variations were due almost entirely to problems with the measurements, not to real variations in the samples. By the early 1960s enough measurements had been made to convince most scientists that in the material to which they had access, terrestrial rocks and meteorites, each element always had the same isotopic composition (except for small fractionations of stable isotopes and shifts 

Element A Atom % Abundance Process Element A Atom% Abundance Process 

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