Molecular nitrogen (N2) comprises three-quarters of Earth’s atmosphere and significant portions of other planetary atmospheres. We report a 19 per mil (‰) excess of 15N15N in air relative to a random distribution of nitrogen isotopes, an enrichment that is 10 times larger than what isotopic equilibration in the atmosphere allows. Biological experiments show that the main sources and sinks of N2 yield much smaller proportions of 15N15N in N2. Electrical discharge experiments, however, establish 15N15N excesses of up to +23‰. We argue that 15N15N accumulates in the atmosphere because of gas-phase chemistry in the thermosphere (>100 km altitude) on time scales comparable to those of biological cycling. The atmospheric 15N15N excess therefore reflects a planetary-scale balance of biogeochemical and atmospheric nitrogen chemistry, one that may also exist on other planets.
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机译：分子氮（N 2 ）占地球大气的四分之三和其他行星大气的大部分。我们报告相对于氮同位素的随机分布，空气中的 15 N 15 N过量19 / mil（‰），这比同位素同位素的富集大10倍大气中的平衡允许。生物实验表明，N 2 的主要来源和汇在N 2 中产生的 15 N 15 N比例要小得多。子>。但是，放电实验确定 15 N 15 N的过量值最高为+ 23‰。我们认为， 15 N 15 N会在大气中积聚，这是由于在热层（> 100 km高度）中的气相化学反应在时间尺度上可与生物循环相比。因此，大气中 15 N 15 N的过量反映了生物地球化学和大气氮化学的行星尺度平衡，这种平衡也可能存在于其他行星上。
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