澳大利亚科廷大学Gamaleldien Hamed团队的一项最新研究提出，地球水文循环始于40亿年前或更早。相关论文发表在2024年6月3日出版的《自然—地球科学》杂志上。

据悉，早期地球上的大气(淡水)水和大陆地壳之间广泛的相互作用可能是生命出现的关键，尽管水文循环何时开始尚不清楚。

该团队研究人员对澳大利亚西部Jack山锆石晶体的氧同位素组成进行了分析，以确定水文循环开始的时间。锆石颗粒的分析显示，在40-39和35-34亿年前的两次岩浆活动，以氧同位素组成低于地幔值(即¹⁸O/¹⁶O比值<5.3±0.6‰，相对于维也纳标准平均海水(2s.d))为特征。¹⁸O/¹⁶O比率的最大负偏约在40和34亿年前，分别低至2.0‰和-0.1‰。

通过Monte Carlo模拟，研究证明了锆石中的这种同位素轻值需要浅层岩浆系统与大气水的相互作用，这种相互作用可能始于40亿年或更早，它们与地球上现存最古老的大陆地壳残余物同时存在。大陆地壳的出现、淡水的存在和水循环的开始，可能促进了地球形成后不到6亿年生命所需的环境生态位的发展。

附：英文原文

Title: Onset of the Earth’s hydrological cycle four billion years ago or earlier

Author: Gamaleldien, Hamed, Wu, Li-Guang, Olierook, Hugo K. H., Kirkland, Christopher L., Kirscher, Uwe, Li, Zheng-Xiang, Johnson, Tim E., Makin, Sean, Li, Qiu-Li, Jiang, Qiang, Wilde, Simon A., Li, Xian-Hua

Issue&Volume: 2024-06-03

Abstract: 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 3.5–3.4billion 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 (2s.d)). The most negative ¹⁸O/¹⁶O ratios at around 4.0 and 3.4billion 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 4.0billion 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 600million years after Earth’s formation.

DOI: 10.1038/s41561-024-01450-0

Source: https://www.nature.com/articles/s41561-024-01450-0