Study Shows Fresh Water Reached Earth from Space Four Billion Years Ago
A chemical analysis of rare and ancient zircon crystals taken from the remote and foreboding Jack Hills of Western Australia is causing scientists to reevaluate their assumptions about when the first fresh water reached the surface of the Earth. This new study, which has just been published in Nature Geoscience, showed that these primordial rocks had absorbed fresh water delivered to the Earth by meteors or other heavenly bodies approximately four billion years ago, or 500 million years earlier than previous estimates. This is just a few hundred million years after the Earth first coalesced into a solid mass.
“We were able to date the origins of the hydrological cycle, which is the continuous process through which water moves around Earth and is crucial for sustaining ecosystems and supporting life on our planet,” study lead author Hamed Gamaleldian, a professor of planetary sciences from Curtin University in Perth, Australia, stated in a Curtin press release detailing the results of his team’s research.
Water did not form on Earth through natural processes, but could only have been delivered by astronomical bodies like meteors and comets that were crashing into the planet on a regular basis long, long ago. The distribution of water across the planet’s surface was one of the precursors that ultimately allowed life to evolve and proliferate, and which allows it to survive to this day.
When the Earth Was an Infant, There Was Land and Fresh Water
For planetary scientists looking to study primordial conditions on the most ancient version of Earth, the dry, rocky wasteland known as the Jack Hills in Western Australia is the ideal destination. In this remote location researchers have found samples of the oldest material known to exist anywhere on Earth, which are crystals of a type of mineral known as zircon. The most ancient samples of zircon discovered in the Jack Hills have been dated to 4.4 billion years ago, which is only 150 million years after the planet first formed.
In the latest study of this earliest of all minerals, a group of scientists from Australia and China used a procedure known as secondary-ion mass spectrometry to examine the chemical makeup of more than 1,400 Jack Hills zircon samples, which ranged in age from 1.85 billion years old and to four billion years old. The goal of this research was to measure the types of oxygen isotopes present in these crystals, to recreate the conditions responsible for their creation.
As expected, the most extraordinarily ancient of these crystals had unique isotopic signatures, described by their discoverers as “extremely isotopically light.”
“Such light oxygen isotopes are typically the result of hot, fresh water altering rocks several kilometers below Earth’s surface,” Dr. Gamaleldian explained.
The lightness of the zircon pieces’ composition indicated they could only have been formed underneath the planet’s crust, in the dense primordial layer of molten magma that hardened on top to form that crust during the Hadean epoch (4.6 billion to four billion years ago). Fresh water delivered by asteroid or meteor showers somehow managed to penetrate to this level of still molten material, and this water left its isotopic imprint in the oldest zircon samples.
What looks like a boring quartzite is actually one of the most important rocks for understanding the early Earth. This is the Jack Hills quartzite of Western Australia. This boring quartzite contains zircon that are as old as 4.4 billion years old. That’s older than Gandalf! pic.twitter.com/UanKKd472d
— Traveling Geologist (@travelinggeolog) August 7, 2019
Previous evidence suggested that the Earth had been covered entirely by a salty ocean four billion years ago. However, the processes that created the zircon crystals beneath the Earth’s crust at that time would not have been possible unless there had been some type of solid surface present. A large mass of land would have been created in this location, with the four-billion-year-old zircon crystals eventually being deposited on the surface, where they would help to form the rocky outcroppings that were destined to become the Jack Hills of Australia.
Texture of the ocean. Evidence has suggested that four billion years ago, the entire surface of the Earth was submerged under a salty ocean. (DAVID/Adobe Stock)
Searching for Life at the Beginning of Earth Time
This surprising find sets back the timeline of the arrival of fresh water to the surface of the Earth, as well as the timeline of the creation of that surface. It also raises the possibility that life evolved on the planet sooner than previously believed.
This discovery not only sheds light on Earth’s early history, but also suggests landmasses and fresh water set the stage for life to flourish within a relatively short time frame—less than 600 million years after the planet formed,” explained Curtin University geoscientist Dr. Hugo Olierook. “The findings mark a significant step forward in our understanding of Earth’s early history and open doors for further exploration into the origins of life.
The earliest signs of life to appear in the fossil record so far were layered, underwater reef-like structures known as stromatolites, which were dated to 3.48 billion years ago and were formed by the metabolic activities of cynobacteria and possibly other microbial lifeforms. These fossilized remnants of living processes are actually the oldest indicators of life found anywhere on the planet, and they were discovered just 500 miles (800 km) north of the Jack Hills.
Rocks in the Pilbara, in Western Australia - the home of the ancient stromatolites, microbial remains. (UNSW)
It is now known that fresh water reached the land surface of the planet at a time when there was only supposed to have been ocean. While this could have been a precursor to the evolution of life at an earlier time, only fossil evidence could prove such a scenario correct, and as of now no such evidence has been recovered. But if such ancient fossils are ever found, it will likely be the Jack Hills region that produces them.
Top image: Clear drop of water, the first of which arrived at Earth 4 billion years ago. Source: willyam/Adobe Stock
By Nathan Falde
