The amount of nitrogen (N₂) present in the atmosphere when life evolved on our planet is central for understanding the production of prebiotic molecules and, hence, is a fundamental quantity to constrain. Estimates of atmospheric molecular nitrogen partial surface pressures during the Archean, however, widely vary in the literature. In this study, we apply a model that combines newly gained insights into atmospheric escape, magma ocean duration, and outgassing evolution. Results suggest <420 mbar surface molecular nitrogen at the time when life originated, which is much lower compared with estimates in previous works and hence could impact our understanding of the production rate of prebiotic molecules such as hydrogen cyanide. Our revised values provide new input for atmospheric chamber experiments that simulate prebiotic chemistry on the early Earth. Our results that assume negligible nitrogen escape rates are in agreement with research based on solidified gas bubbles and the oxidation of iron in micrometeorites at 2.7 Gyr ago, which suggest that the atmospheric pressure was probably less than half the present-day value. Our results contradict previous studies that assume N₂ partial surface pressures during the Archean were higher than those observed today and suggest that, if the N₂ partial pressure were low in the Archean, it would likely be low in the Hadean as well. Furthermore, our results imply a biogenic nitrogen fixation rate from 9 to 14 Teragram N₂ per year (Tg N₂/year), which is consistent with modern marine biofixation rates and, hence, indicate an oceanic origin of this fixation process.

中文翻译：

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地球上生命进化时的大气氮

氮量（N ₂) 存在于我们星球上生命进化时的大气中，对于理解益生元分子的产生至关重要，因此是一个需要限制的基本量。然而，对太古代大气分子氮表面分压的估计在文献中差异很大。在这项研究中，我们应用了一个模型，该模型结合了对大气逃逸、岩浆海洋持续时间和除气演化的新见解。结果表明，生命起源时表面分子氮小于 420 mbar，与之前工作中的估计值相比要低得多，因此可能会影响我们对诸如氰化氢等益生元分子生产率的理解。我们修订后的值为模拟早期地球上的生命前化学的大气室实验提供了新的输入。我们假设氮逸出率可以忽略不计的结果与基于固化气泡和 2.7 Gyr 前微陨石中铁的氧化的研究一致，这表明大气压力可能小于当前值的一半。我们的结果与先前假设 N₂太古代的表面分压高于今天观察到的那些，这表明，如果太古代的 N ₂分压低，那么冥界的 N ₂分压也可能低。此外，我们的结果表明生物固氮率为每年 9 至 14 Teragram N ₂ (Tg N ₂ /年)，这与现代海洋生物固定率一致，因此表明该固定过程起源于海洋。