Ancient Martian nitrogen

The isotopic signatures and elemental ratios of nitrogen, argon and xenon determined in shock-melted glass in shergottite meteorites were found to closely resemble the Viking spacecraft data for the present Martian atmosphere. Searches for early signatures, before the Martian atmosphere was subjected to fractionation mechanisms, can be carried out on Martian meteorite ALH84001 and show that nitrogen signatures are incompatible with those of the present atmosphere. We report here the identification of two ancient, a distinctly light and an only slightly evolved, nitrogen isotopic signatures (δ¹⁵N = -30 ‰ and +4 ‰, respectively), as well as a correlation with the isotope ratio ¹²⁹Xe/¹³²Xe. Since this ratio evolved rapidly during the early history, due to the short (16 million year) half-life of the extinct precursor ¹²⁹I, it serves as a useful time marker.