Fresh water on Earth four billion years ago

The operation of a hydrological cycle (i.e., exchange of water between the land, oceans, and atmosphere) has significant implications for the emergence of life. The oldest confirmed single-celled organisms at ~3.48 billion years ago (Ga) (Pilbara Craton, Western Australia) are thought to have formed in the presence of meteoric (fresh) water on emerged (subaerial) land in a hot spring environment. However, when widespread interaction between fresh water and emerged continental crust first began is poorly constrained. In this study, we use >1000 oxygen isotope analyses of Jack Hills detrital zircon to track fluid-rock interactions from the Hadean to the Paleoarchean (~4.4–3.1 Ga). We identify extreme isotopically light O (i.e., δ18O < 4.0 ‰) values older than 3.5 Ga. The data define two periods of magmatism with extreme isotopically-light O as low as 2.0 ‰ and –0.1 ‰ at around 4.0 and 3.4 Ga, respectively. Using Monte Carlo simulations, we demonstrate that such values can only be generated by the interaction of crustal magmatic systems with meteoric water. Our data constrains the earliest emergence of continental crust on Earth, the presence of fresh water, and the start of the hydrological cycle that likely provided the environmental niches required for a life less than 600 million years after Earth’s accretion.