Helium isotopic ratios in carbonaceous chondrites: Significant for the early solar nebula and circumstellar diamonds?

Introduction: A confusingly large number of noble gas components has been found in meteorites, based on distinct compositions, origins, carrier phases, or release characteristics [1]. The discovery that the carriers of the primordial noble gases survive acid treatment [2] led to the identification of several circumstellar grain types [3]. The oxidisable carbonaceous carrier “phase Q”, however, which contains most of the isotopically “normal” Ar-Xe in acid-resistant residues has not been identified yet [see 4 for references].