Abstract Phosphorus (P) is the key nutrient thought to limit primary productivity on geological timescales. Phosphate levels in Archean marine sediments are low, but quantification of the P cycle and how it changed through a billion years of recorded Archean history remain a challenge, hindering our understanding of the role played by P in biosphere/geosphere co-evolution on the early Earth. Here, we design kinetic and thermodynamic models to quantitatively assess one key component of the early P cycle – continental weathering – by considering the emergence and elevation of continents, as well as the evolution of climate, the atmosphere, and the absence of macroscopic vegetation during the Archean Eon. Our results suggest that the weathering rate of apatite, the major P-hosting mineral in the rocks, was at least five times higher in the Archean Eon than today, attributable to high levels of pCO2,g. Despite this, the weathering flux of P to the oceans was negligible in the early Archean Eon, increasing to a level comparable to or greater than the modern by the end of eon, a consequence of accelerating continental emergence. Furthermore, our thermodynamic calculations indicate high solubilities of primary and secondary P-hosting minerals in the acidic weathering fluids on land, linking to high Archean pCO2,g. Thus, weathering of P was both kinetically and thermodynamically favorable on the Archean Earth, and river water could transport high levels of dissolved P to the oceans, as also supported by the observed P-depletion in our new compilation of Archean paleosols. Lastly, we evaluated the relative rates of physical erosion and chemical weathering of silicates during the Archean Eon. The results suggest that continental weathering on the early and middle Archean Earth might have been transport-limited due to low erosion rates associated with limited subaerial emergence and low plateau elevations; by the late Archean, however, continental weathering would have transited to kinetically-limited state because of continental emergence, increased plateau elevation, and weakening weathering rates. Overall, our weathering calculations together with paleosol evidence indicate an increasing flux of bioavailable P to the oceans through time, associated with late Archean continental emergence, reaching levels comparable to or higher than modern values by the end of the eon. Increased P fluxes could have fueled increasing rates of primary production, including oxygenic photosynthesis, through time, facilitating the irreversible oxidation of the Earth’s atmosphere early in the Proterozoic Eon.

中文翻译：

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太古宙地球上的循环磷：第一部分。大陆风化和磷的河流运输

摘要 磷 (P) 是被认为在地质时间尺度上限制初级生产力的关键营养素。太古代海洋沉积物中的磷酸盐含量很低，但对 P 循环的量化以及它如何在 10 亿年的太古代历史记录中发生变化仍然是一个挑战，阻碍了我们对 P 在早期生物圈/地圈协同进化中的作用的理解地球。在这里，我们设计了动力学和热力学模型，通过考虑大陆的出现和海拔，以及气候、大气的演变以及在此期间宏观植被的缺失，来定量评估早期 P 循环的一个关键组成部分——大陆风化。太古宙。我们的结果表明，磷灰石（岩石中主要的含磷矿物）的风化速率，由于 pCO2,g 的高水平，太古宙中的温度至少比今天高出五倍。尽管如此，在太古宙早期，P 到海洋的风化通量可以忽略不计，到 eon 末期增加到与现代相当或更高的水平，这是大陆出现加速的结果。此外，我们的热力学计算表明，原生和次生含磷矿物在陆地酸性风化流体中具有高溶解度，这与高太古代 pCO2,g 相关。因此，在太古代地球上，P 的风化在动力学和热力学上都是有利的，河水可以将大量溶解的 P 输送到海洋，这也得到了我们新的太古代古土壤汇编中观察到的 P 消耗的支持。最后，我们评估了太古宙期间硅酸盐的物理侵蚀和化学风化的相对速率。结果表明，早期和中期太古宙地球上的大陆风化可能受到运输限制，这是由于与地面出现有限和高原海拔低相关的低侵蚀率；然而，到太古代晚期，由于大陆出现、高原海拔增加和风化率减弱，大陆风化作用将转变为动力学限制状态。总体而言，我们的风化计算以及古土壤证据表明，随着时间的推移，海洋中生物可利用 P 的通量不断增加，这与太古宙晚期大陆出现有关，到世纪末达到或高于现代值的水平。