Solar radiation and geological processes over the first few million years of Earth’s history, followed soon thereafter by the origin of life, steered our planet towards an evolutionary trajectory of long-lived habitability that ultimately enabled the emergence of complex life. We review the most important conditions and feedbacks over the first 2 billion years of this trajectory, which perhaps represent the best analogue for other habitable worlds in the galaxy. Crucial aspects included: (1) the redox state and volatile content of Earth’s building blocks, which determined the longevity of the magma ocean and its ability to degas H 2 O and other greenhouse gases, in particular CO 2 , allowing the condensation of a water ocean; (2) the chemical properties of the resulting degassed mantle, including oxygen fugacity, which would have not only affected its physical properties and thus its ability to recycle volatiles and nutrients via plate tectonics, but also contributed to the timescale of atmospheric oxygenation; (3) the emergence of life, in particular the origin of autotrophy, biological N 2 fixation, and oxygenic photosynthesis, which accelerated sluggish abiotic processes of transferring some volatiles back into the lithosphere; (4) strong stellar UV radiation on the early Earth, which may have eroded significant amounts of atmospheric volatiles, depending on atmospheric CO 2 /N 2 ratios and thus impacted the redox state of the mantle as well as the timing of life’s origin; and (5) evidence of strong photochemical effects on Earth’s sulfur cycle, preserved in the form of mass-independent sulfur isotope fractionation, and potentially linked to fractionation in organic carbon isotopes. The early Earth presents itself as an exoplanet analogue that can be explored through the existing rock record, allowing us to identify atmospheric signatures diagnostic of biological metabolisms that may be detectable on other inhabited planets with next-generation telescopes. We conclude that investigating the development of habitable conditions on terrestrial planets, an inherently complex problem, requires multi-disciplinary collaboration and creative solutions.

中文翻译：

---

对地球的使命：最初的 20 亿年

地球历史最初几百万年的太阳辐射和地质过程，紧随其后的是生命的起源，将我们的星球引向了长期宜居的进化轨迹，最终促成了复杂生命的出现。我们回顾了这条轨迹前 20 亿年中最重要的条件和反馈，这可能代表了银河系中其他宜居世界的最佳模拟。关键方面包括：(1) 地球构建块的氧化还原状态和挥发物含量，这决定了岩浆海洋的寿命及其脱气 H 2 O 和其他温室气体，特别是 CO 2 的能力，从而使水凝结海洋; (2)所得脱气地幔的化学性质，包括氧逸度，这不仅会影响它的物理特性，从而影响它通过板块构造回收挥发物和营养物质的能力，还会影响大气氧化的时间尺度；(3) 生命的出现，特别是自养、生物固氮和含氧光合作用的起源，加速了缓慢的将一些挥发物转移回岩石圈的非生物过程；(4) 早期地球上强烈的恒星紫外线辐射，可能已经侵蚀了大量的大气挥发物，这取决于大气中的CO 2 /N 2 比率，从而影响地幔的氧化还原状态以及生命起源的时间；(5) 以与质量无关的硫同位素分馏形式保存的对地球硫循环的强烈光化学影响的证据，并可能与有机碳同位素的分馏有关。早期地球将自己呈现为一个系外行星类似物，可以通过现有的岩石记录进行探索，使我们能够识别诊断生物代谢的大气特征，这些特征可以在其他有人居住的行星上用下一代望远镜检测到。我们得出的结论是，调查类地行星宜居条件的发展是一个固有的复杂问题，需要多学科合作和创造性的解决方案。