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 (1σ). The model projects that a deoxygenation of the atmosphere, with atmospheric O₂ dropping sharply to levels reminiscent 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.

地球的现代大气是高度含氧的，是其地表生物圈的一个可远程探测到的信号。然而，地球大气中氧基生物特征的寿命仍然不确定，尤其是在遥远的未来。在这里，我们使用组合的生物地球化学和气候模型来检查地球上富氧大气条件的可能时间尺度。使用随机方法，我们发现地球大气层的平均未来寿命为 1.08 ± 1.4 亿年 (1 σ )，氧气含量超过当前大气水平的 1%。该模型预测大气脱氧，大气中的 O ₂急剧下降到让人想起太古代地球的水平，最有可能在地球气候系统中潮湿的温室条件开始之前以及大气中地表水的大量流失之前触发。我们发现，未来的脱氧是太阳通量增加的必然结果，而其精确时间则受地幔和海洋-大气-地壳系统之间还原能量的交换通量的调节。我们的结果表明，行星碳酸盐-硅酸盐循环将趋向于最终导致 CO ₂- 有限的生物圈和快速的大气脱氧，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宜居性末期的潜在重要性。