Carbon isotope ratios for uracil and xanthine of δ13C = +44.5 ‰ and +37.7 ‰ , respectively , indicate a non-terrestrial origin for these compounds .
Carbon isotope ratios for uracil and xanthine of 44.5 ‰ and +37.7 ‰ , respectively , indicate a non-terrestrial origin for these compounds .