Earth's atmospheric composition during the Archean eon of 4 to 2.5 billion years ago has few constraints. However, the geochemistry of recently discovered iron-rich micrometeorites from 2.7 billion-year-old limestones could serve as a proxy for ancient gas concentrations. When micrometeorites entered the atmosphere, they melted and preserved a record of atmospheric interaction. We model the motion, evaporation, and kinetic oxidation by CO2 of micrometeorites entering a CO2-rich atmosphere. We consider a CO2-rich rather than an O2-rich atmosphere, as considered previously, because this better represents likely atmospheric conditions in the anoxic Archean. Our model reproduces the observed oxidation state of micrometeorites at 2.7 Ga for an estimated atmospheric CO2 concentration of >70% by volume. Even if the early atmosphere was thinner than today, the elevated CO2 level indicated by our model result would help resolve how the Late Archean Earth remained warm when the young Sun was ~20% fainter.

中文翻译：

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从微陨石氧化推断出27亿年前的大气CO2水平。

在4至25亿年前的太古代时期，地球的大气成分几乎没有限制。但是，最近发现的来自27亿年前的石灰岩的富铁微陨石的地球化学可以替代古代气体的浓度。当微陨石进入大气时，它们融化并保存了大气相互作用的记录。我们对进入富含CO2的大气中的微陨石的CO2进行运动，蒸发和动力学氧化进行建模。如前所述，我们考虑的是富含CO2的气氛，而不是富含O2的气氛，因为这更好地代表了缺氧太古宙中可能的大气条件。我们的模型再现了在2.7 Ga下观察到的微陨石的氧化态，估计大气中的CO2浓度> 70％（体积）。