地球含氧大气的未来寿命
The future lifespan of Earth's oxygenated Atmosphere
摘要：
地球的现代大气是高度含氧的，是其表面生物圈的远程可检测信号。然而，地球大气中基于氧的生物特征的寿命仍然不确定，特别是在遥远的未来。在这里，我们使用一个结合地球化学和气候模型来研究地球上富氧大气条件的可能时间尺度。使用随机方法，我们发现，平均未来寿命的地球大气中的氧气含量超过1%的目前的大气水平是10.8 +-0.14亿年。该模型预测，在地球气候系统中潮湿的温室条件开始之前，以及在大气层中大量流失地表水之前，大气层的脱氧作用很可能会被触发，大气层中的氧气含量急剧下降到令人回想起的地球水平。我们发现，未来的脱氧是一个不可避免的结果，增加太阳通量，而其精确的时间是调制的地幔和海洋-大气-地壳系统之间的还原力的交换通量。我们的研究结果表明，行星碳酸盐-硅酸盐循环将倾向于导致最终CO2限制生物圈和快速大气脱氧，强调需要适用于弱氧和缺氧系外行星大气的强大大气生物特征，并强调大气有机雾霾在行星可居住性的终端阶段的潜在重要性。
英文摘要：
Earth's modern atmosphere is highly oxygenated and is a remotely detectable signal of its surface biosphere. However, the lifespan of oxygen-based biosignatures in Earth's atmosphere remains uncertain, particularly for the distant future. Here we use a combined biogeochemistry and climate model to examine the likely timescale of oxygen-rich atmospheric conditions on Earth. Using a stochastic approach, we find that the mean future lifespan of Earth's atmosphere with oxygen levels more than 1% of the present atmospheric level is 1.08+-0.14 billion years. The model projects that a deoxygenation of the atmosphere, with atmospheric oxygen dropping sharply to levels reminiscnet of the Archaean Earth, will most probably be triggered before the inception of moist greenhouse conditions in Earth's climate system and before the extensive loss of surface water from the atmosphere. We find that future deoxygenation is an inevitable consequence of increasing solar fluxes, whereas its precise timing is modulated by the exchange flux of reducing power between the mantle and the ocean-atmosphere-crust system. Our results suggest that the planetary carbonate-silicate cycle will tend to lead to terminally CO2-limited biospheres and rapid atmospheric deoxygenation, emphasizing the need for robust atmospheric biosignatures applicable to weakly oxygenated and anoxic exoplanet atmospheres and highlighting the potential importance of atmospheric organic haze during the terminal stages of planetary habitability.
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