A new study shows that the Earth’s surface was first sprinkled with fresh water about 4 billion years ago, or about 500 million years earlier than previously thought. A team of researchers from Australia and China used oxygen isotopes trapped in ancient minerals to determine when the first signs of fresh water might have moistened the skin of our newborn planet.

The Jack Hills in Western Australia preserve the oldest surviving shell material. For 4.4 billion years, primitive minerals remained relatively unchanged under the influence of heat and pressure.

There isn’t much water in today’s dry, red, dusty landscape, but scientists have found evidence of Earth’s first rains trapped in Hadean zircon crystals, dramatically changing our understanding of the planet’s hydrological history.

“By examining age and oxygen isotopes in small crystals in the mineral zircon, we found extremely light isotope signatures going back as much as four billion years,” says lead author Hamed Gamaleldien, a geologist at Curtin University in Australia.

Gamaleldien and colleagues used secondary ion mass spectrometry to analyze small zircon grains and determine which oxygen isotopes were present in the magma where the crystals formed.

Jack Hills zircons had an “isotopically extremely light” composition; this would only be possible if they formed beneath the mantle and were also exposed to fresh water, particularly meteoric water that had recently fallen from the sky. So being locked inside these crystals could be evidence of Earth’s first rains penetrating shallow regions of its newly solidified crust.

“Such light oxygen isotopes are typically the result of hot fresh water altering rocks several kilometers below the Earth’s surface,” says Gamaleldien. “Evidence of fresh water this deep in the Earth casts doubt on the current theory that the Earth was completely covered by an ocean four billion years ago.”

Geologist and co-author Hugo Oliruk from Curtin University states that this research has implications for many areas of science.

“This discovery not only sheds light on Earth’s early history, but also suggests that land and fresh water laid the groundwork for the development of life in a relatively short period of time – less than 600 million years after the planet formed,” he says.

It was previously believed that the shell was buried beneath the ocean; Some of the oldest terrestrial life forms we have found are 3.48 billion-year-old microbial reefs known as stromatolites, located 800 kilometers (about 500 miles) north of the Jack Hills in the Pilbara Craton.

But this new study shows that soil, freshwater reserves, the water cycle, and perhaps even life on Earth emerged much earlier than we thought. It also supports the “cold early Earth” theory explained by University of Wisconsin-Madison geophysicist John Valley, who called Hadea zircons the oldest material on Earth in his 2014 paper.

The theory suggests that shortly after the planet’s sea of ​​molten rock solidified in the crust, Earth became cold enough to host liquid water, oceans, and the hydrosphere.

“These findings mark a significant step forward in our understanding of Earth’s early history and open the door to further research into the origins of life,” says Oliruk. This study was published on: Natural Geology.