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Principal constituent of the Earth’s atmosphere (78.08 vol. % at ground level). Nitrogen is the fifth most abundant element in the universe by atom abundance. Nitrogen comprises only 3.5 vol. % of the atmosphere of Venus and 2.7 vol. % of Mars’s atmosphere. Nitrogen has two isotopes: 14N (99.632 %) and 15N (0.368 %). Nitrogen isotopic variations are reported as δ15N in parts per thousand (‰) deviations from the nitrogen isotopic composition of Earth’s atmosphere (15N/14N = 0.003676).

Large N isotopic variations are observed in the solar system from -250 ‰ (lowest values in lunar soils) to 1600 ‰ (bencubinites). Comets Hale-Bopp and LINEAR have essentially identical δ15N values of ~940 ‰. Values of δ15N in the lunar regolith show a very large range from ~100 ‰ to -250 ‰ with ratios appearing to vary with age. The lunar results can be explained by secular variation in δ15N of the solar wind over time, although this hypothesis conflicts with the apparent stability of ratios in other solar wind volatile elements. Alternatively, the variation could result from mixing in a non-solar wind component (meteorite or comet material deposited on the moon during impacts). Extreme δ15N variations have been documented in organic material from meteorites (image of insoluble organic matter extracted from the CR chondrite EET 92042).

Some or all content above used with permission from J. H. Wittke.