Comment on “summary and implications of reported amino acid concentrations in the Murchison meteorite” by E. L. Shock and M. D. Schulte

Abstract

A criticism of the claim by Shock and Schulte (1990) that there is a correlation between the amino acid abundances (relative to glycine) in the Murchison meteorite and their aqueous solubilities is presented. Their suggestion that 'the same factors which control the aqueous solubility of many amino acids also control their relative abundances in the Murchison meteorite is argued to be incorrect. It is proposed that even though the water/meteorite ratio would have been less during meteorite aqueous alteration than that in the 100-C laboratory extraction procedure, amino acids are simply too soluble. The distribution of other meteorite organic components such as PAHs may have been affected by alteration because they are only slightly soluble in water and can be easily separated by geochromatographic processes. In their reply Shock and Schulte contend that the critics argue against a point not made in their paper and that their argument was supported with several unsubstantiated assertions, including an unfounded claim that the temperature dependence of amino acid solubilities are 'not greatly different', a misrepresentation of isopiestic studies on concentration solutions as equilibrium solubility measurements.