Assertion: purine | /r/HasProperty | van der velden
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Source sentences:
text: Subsequent studies of formic acid extracts have identified several purines, including adenine, guanine, hypoxanthine, xanthine, and the pyrimidine uracil in the CM2 meteorites Murchison and Murray, and the CI1 Orgueil (Stoks and Schwartz, 1981; Van der Velden and Schwartz, 1977), with total abundances around 1 part-per-million.