Widespread interaction between meteoric (fresh) water and emerged continental crust on the early Earth may have been key to the emergence of life, although when the hydrological cycle first started is poorly constrained. Here we use the oxygen isotopic composition of dated zircon crystals from the Jack Hills, Western Australia, to determine when the hydrological cycle commenced. The analysed zircon grains reveal two periods of magmatism at 4.0–3.9 and 3.5–3.4 billion years ago characterized by oxygen isotopic compositions below mantle values (that is,¹⁸O/¹⁶O ratios <5.3 ± 0.6‰ relative to Vienna Standard Mean Ocean Water (2 s.d)). The most negative ¹⁸O/¹⁶O ratios at around 4.0 and 3.4 billion years ago are as low as 2.0‰ and –0.1‰, respectively. Using Monte Carlo simulations, we demonstrate that such isotopically light values in zircon require the interaction of shallow crustal magmatic systems with meteoric water, which must have commenced at or before 4.0 billion years ago, contemporaneous with the oldest surviving remnant of Earth’s continental crust. The emergence of continental crust, the presence of fresh water and the start of the hydrological cycle probably facilitated the development of the environmental niches required for life fewer than 600 million years after Earth’s formation.

大气（淡水）和早期地球上出现的大陆地壳之间广泛的相互作用可能是生命出现的关键，尽管水文循环最初开始的时间受到很少的限制。在这里，我们使用来自西澳大利亚州杰克山的已测年锆石晶体的氧同位素组成来确定水文循环的开始时间。分析的锆石颗粒揭示了 4.0–3.9 和 3.5–34 亿年前的两个岩浆活动时期，其特征是氧同位素组成低于地幔值（即¹⁸ O/ ¹⁶ O 比率 <5.3 ± 0.6‰ 相对于维也纳标准平均值）海水（2 SD））。大约 4.0 亿年前和 34 亿年前， ¹⁸ O/ ¹⁶ O 比率最负值分别低至 2.0 ‰ 和 –0.1 ‰。通过蒙特卡罗模拟，我们证明了锆石中的这种同位素轻值需要浅地壳岩浆系统与大气水的相互作用，这种相互作用必须在 40 亿年前或之前开始，与地球大陆地壳最古老的残余物同时期。在地球形成后不到 6 亿年的时间内，大陆地壳的出现、淡水的出现以及水文循环的开始可能促进了生命所需环境生态位的发展。