Origin of freshwater on Earth pushed back half a billion years to about 4 billion years ago

Amazing stuff!

"... New research led by geologists at Western Australia’s Curtin University provides evidence that fresh water emerged on Earth about 4 billion years ago – half a billion years earlier than previously thought. ...
The  geologists examined ancient crystals from the Jack Hills in Western Australia, about 650km north of the state capital, Perth. The rocks in the formation are 4.4 billion years old, making them the oldest terrestrial material on Earth – our planet itself is 4.543 billion years old. ...

“By examining the oxygen isotopes in crystals of the mineral zircon, we found unusually light isotopic signatures as far back as 4 billion years ago. Such light oxygen isotopes are typically the result of hot, fresh water altering rocks several kilometres below Earth’s surface,” ...

“Evidence of fresh water this deep inside Earth challenges the existing theory that Earth was completely covered by ocean 4 billion years ago.” ..."

From the 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 3.5–3.4 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."

Origin of freshwater on Earth pushed back half a billion years

Fresh findings: earliest evidence of life-bringing fresh water on Earth (original press release) New Curtin-led research has found evidence that fresh water on Earth, which is essential for life, appeared about four billion years ago – five hundred million years earlier than previously thought.

Onset of the Earth’s hydrological cycle four billion years ago or earlier (no public access)

Fig. 1: Jack Hills zircon δ18O versus age for individual magmatic grains (thank the journal for the blurriness of this image).