Historical Information on Solar Abundances of the ElementsHistorical Info Evidence Conclusions
Noting that the Earth's crust and the Sun's gaseous envelope may not represent the overall compositions of these bodies, Harkins  showed in 1917 that 99% of the material in ordinary meteorites consists of seven, even-numbered elements - Fe, O, Ni, Si, Mg, S and Ca. He concluded that "... in the evolution of elements much more material has gone into the even-numbered elements than into those which are odd ..." (p. 869). In the 1920s, Payne  and Russell  showed that the solar atmosphere is mostly H and He, and in 1938 Goldschmidt  proposed an abundance table based on stellar spectra for volatile elements and on meteorites for nonvolatile elements. However, Hoyle  and other astronomers continued to believe until the end of World War II that "... the Sun was made mostly of iron ..." (p. 153). Research on H-fusion at Los Alamos during the War  likely aided their conversion.
Goldschmidt's proposed loss of light, volatile elements from meteorites and rocky planets  is reasonable from the view of cosmic evolution, but from the view of nuclear physics the difference between an Fe-rich and a H-rich Sun is drastic. Iron is an even-numbered element. It consists mostly of Fe-56, with an ordinary charge density, Z/A = 0.46, and the lowest  mass per nucleon, M/A. Hydrogen is an odd-numbered element. It consists mostly of H-1, with the highest values of Z/A and M/A among stable nuclides . The H-rich Sun thus violates, on a grand scale, Harkins' prediction  (p. 859) that "... the more stable atoms should be more abundantly formed ...", but fine structure abundance peaks are still assigned to nuclear stability (e.g., Suess & Urey ). To explain an H-rich Sun, Burbidge et al.  and Cameron  assumed that the products of nucleosynthesis were mixed back into the interstellar medium before the solar system formed.
The discovery  of radiogenic Xe-129 in meteorites  severely constrained the time for mixing. The mixing time essentially vanished as Reynolds' mass spectrometer  and others revealed the decay products of many short-lived nuclides and isotopic anomalies from nucleosynthesis as regular components of meteorites. As a graduate student, Manuel joined Kuroda's effort to decipher isotope abundances in 1960, and in 2000 he officially retired as Professor and Department Chairman. The evidence he found for an iron-rich Sun is summarized in Section II, in a 1998 review , and in the proceedings of an ACS symposium  organized by Seaborg and Manuel in August, 1999. The conclusion that a hydrogen-filled Sun is obsolete, related observations, and the status of work on remaining issues are given in Section III.
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