Stellar evolution models predict that the solar luminosity was lower in the past, typically 20-25% lower during the Archean (3.8-2.5 Ga). Despite the fainter Sun, there is strong evidence for the presence of liquid water on Earth’s surface at that time. This “faint young Sun problem” is a fundamental question in paleoclimatology, with important implications for the habitability of the early Earth, early Mars and exoplanets. Many solutions have been proposed based on the effects of greenhouse gases, atmospheric pressure, clouds, land distribution and Earth’s rotation rate. Here we review the faint young Sun problem for Earth, highlighting the latest geological and geochemical constraints on the early Earth’s atmosphere, and recent results from 3D global climate models and carbon cycle models. Based on these works, we argue that the faint young Sun problem for Earth has essentially been solved. Unfrozen Archean oceans were likely maintained by higher concentrations of CO 2 , consistent with the latest geological proxies, potentially helped by additional warming processes. This reinforces the expected key role of the carbon cycle for maintaining the habitability of terrestrial planets. Additional constraints on the Archean atmosphere and 3D fully coupled atmosphere-ocean models are required to validate this conclusion.

中文翻译：

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地球的微弱年轻太阳问题解决了吗？

恒星演化模型预测，过去的太阳光度较低，在太古代 (3.8-2.5 Ga) 期间通常会降低 20-25%。尽管太阳较暗，但有强有力的证据表明当时地球表面存在液态水。这个“微弱的年轻太阳问题”是古气候学中的一个基本问题，对早期地球、早期火星和系外行星的宜居性具有重要意义。基于温室气体、大气压力、云层、土地分布和地球自转速率的影响，已经提出了许多解决方案。在这里，我们回顾了地球的微弱年轻太阳问题，强调了早期地球大气的最新地质和地球化学限制，以及 3D 全球气候模型和碳循环模型的最新结果。基于这些作品，我们认为地球的暗淡年轻太阳问题已基本解决。未冻结的太古代海洋可能由较高浓度的 CO 2 维持，这与最新的地质代理一致，可能是由于额外的变暖过程。这加强了碳循环在维持类地行星宜居性方面的预期关键作用。需要对太古代大气和 3D 完全耦合的大气-海洋模型进行额外的约束来验证这一结论。