Abiotic ammonium formation in the presence of Ni-Fe metals and alloys and its implications for the Hadean nitrogen cycle

Experiments with dinitrogen-, nitrite-, nitrate-containing solutions were conducted without headspace in Ti reactors (200°C), borosilicate septum bottles (70°C) and HDPE tubes (22°C) in the presence of Fe and Ni metal, awaruite (Ni80Fe20) and tetrataenite (Ni50Fe50). In general, metals used in this investigation were more reactive than alloys toward all investigated nitrogen species. Nitrite and nitrate were converted to ammonium more rapidly than dinitrogen, and the reduction process had a strong temperature dependence. We concluded from our experimental observations that Hadean submarine hydrothermal systems could have supplied significant quantities of ammonium for reactions that are generally associated with prebiotic synthesis, especially in localized environments. Several natural meteorites (octahedrites) were found to contain up to 22 ppm Ntot. While the oxidation state of N in the octahedrites was not determined, XPS analysis of metals and alloys used in the study shows that N is likely present as nitride (N3-). This observation may have implications toward the Hadean environment, since, terrestrial (e.g., oceanic) ammonium production may have been supplemented by reduced nitrogen delivered by metal-rich meteorites. This notion is based on the fact that nitrogen dissolves into metallic melts

Nitrogen isotope variations in the solar system

International audienceThe relative proportion of the two isotopes of nitrogen (14N and 15N) shows dramatic variations among the different solar system objects and reservoirs. NASA's Genesis mission, which provided the first direct sample of the solar wind, confirmed that the Sun, and by inference the protosolar nebula, is highly depleted in the heavy 15N isotope. The inner planets, asteroids, and comets are enriched in 15N by tens to 5 hundreds of percent, with organic matter in primitive meteorites recording the most extreme 15N/14 N ratios. Several lines of evidence suggest that these 15N enrichments were not inherited from presolar material but are, instead, the result of N isotope fractionation processes that occurred early in solar system history. Together, these observations indicate that N isotopes are a powerful tool to investigate early material processing and large-scale disk dynamics as well as planetary formation processes. In addition, N isotopes are the tracer of choice to investigate the origin and evolution of planetary atmospheres