Volcanic gases supplied a large part of Earth's early atmosphere, but constraints on the value of this flux are scarce. Here we model how C-O-H outgassing could have evolved through the late Hadean and early Archean, under the conditions that global plate tectonics had not yet initiated, all outgassing was subaerial, and graphite was the stable carbon phase in the melt source regions. The model fully couples numerical mantle convection, partitioning of volatiles into the melt, and chemical speciation in the gas phase. The mantle oxidation state (which may not have reached late Archean values in the Hadean) is the dominant control on individual species' outgassing rates because it affects both the carbon content of basaltic magmas and the speciation of degassed volatiles. Volcanic gas from mantles more reduced than the iron-wüstite mineral redox buffer would contain virtually no CO₂ because (i) carbonate ions dissolve in magmas only in very limited amounts, and (ii) almost all degassed carbon takes the form of CO instead of CO₂. For oxidised mantles near the quartz-fayalite-magnetite buffer, we predict median CO₂ outgassing rates of less than approximately 5 Tmol yr⁻¹, still lower than the outgassing rates used in many Archean climate studies. Relatively weak outgassing is due in part to the redox-limited CO₂ contents of graphite-saturated melts, and also to a stagnant lid regime's inefficient replenishment of upper mantle volatiles. Our results point to certain chemical and geodynamic prerequisites for sustaining a clement climate with a volcanic greenhouse under the Faint Young Sun.

火山气体提供了地球早期大气的大部分，但对这种通量值的限制很少。在这里，我们模拟了在全球板块构造尚未开始的条件下，COH 脱气如何在晚冥古宙和早期太古代演化，所有脱气都是地下的，石墨是熔体源区域中的稳定碳相。该模型将数值地幔对流、挥发物分配到熔体中以及气相中的化学形态完全耦合。地幔氧化态（可能未达到冥界晚期太古代值）是单个物种脱气速率的主要控制因素，因为它影响玄武岩岩浆的碳含量和脱气挥发物的物种形成。₂因为 (i) 碳酸根离子仅以非常有限的量溶解在岩浆中，并且 (ii) 几乎所有脱气的碳都以 CO 的形式而不是 CO ₂的形式出现。对于石英-铁橄榄石-磁铁矿缓冲区附近的氧化地幔，我们预测 CO ₂中值放气率小于约 5 Tmol yr ^-1，仍低于许多太古代气候研究中使用的放气率。相对较弱的除气部分是由于石墨饱和熔体的氧化还原限制的 CO ₂含量，以及停滞的盖子状态对上地幔挥发物的低效补充。我们的研究结果指出了在微弱的年轻太阳下通过火山温室维持气候的某些化学和地球动力学先决条件。