Art Courtesy of Yurou Liu.
In 1990, NASA’s Voyager 1 spacecraft captured a vast image of local space. Against the cosmos is a speck—a faint blue group of pixels, affectionately known as “The Pale Blue Dot,” or more simply, Earth. Earth is characterized not just by its location in the solar system but also for the life-sustaining substance that gives it its distinctive, pale blue color: water. But when this water originated on the planet is a mystery.
In newly published research, geologists have added a prequel to our understanding of water’s history. Hamed Gamaleldien, along with a team of fellow scientists from Curtin University in Australia, uncovered evidence that freshwater arose on Earth four billion years ago—five hundred million years earlier than previously thought. This means that life could have emerged on Earth earlier than expected.
Gamaleldien described the satisfaction he finds in this new discovery. “To start from looking at my own life and then push the start of all life back by five hundred million years—it’s so exciting,” Gamaleldien said. The sign for when freshwater first emerged came from ancient rocks in the Jack Hills in Western Australia. When Gamaleldien was a PhD student, the chair of his thesis panel, Simon A. Wilde, led him to the Jack Hills to solve the mystery of the origin of ancient water. Wilde had been excavating samples of the mineral zircon in that region since 1983.
“There was a very unsuccessful first year,” Wilde said. “But in 1984, we sort of hit the jackpot, and that’s when we found what was then the oldest crystal on Earth.” They found zircon. Zircon is one of the gold standards in geochemistry research, both because it contains uranium utilized for specific dating and because it remains stable throughout time. One crystal of zircon can resist change across eons of metamorphisms and weathering.
In the new research, Gamaleldien and the team analyzed the oxygen isotopes in zircon crystals that they established to be up to four billion years old. Oxygen has two major isotopes, and when comparing the prevalence of each, scientists can observe distinct ratios arising from freshwater and saltwater environments. Based on around fifteen hundred isotope analyses and statistical simulations, it was found that these zircon crystals were exposed to a mixture of salt and freshwater four billion years ago.
As anyone’s daily water usage can attest, water is connected to a much larger story of our planet and life itself. Freshwater cycles through the atmosphere and percolates through the ground in the hydrological cycle, a process necessary for the origin of life. Based on the information from the oxygen isotopes, the researchers concluded that the hydrological cycle began at least four billion years ago. That idea is still controversial to some scientists, as it would shift the timeline for the origin of life to less than six hundred million after Earth formed, a relatively short period in geological time. The oxygen isotope ratios that correlate with salt and freshwater are based on modern data, so it is impossible to guarantee that these ratios have been constant throughout time. Still, the team hopes their research will reveal insights into the origin of life on Earth.
“Do we have evidence that life started four billion years [before] now?” Gamaleldien said. “We don’t know. But we [had] the recipe. We [had] the ingredients and the main recipes to form life, which is dry land and freshwater, and this was the main implication of our discovery.”
Another recent research paper out of the Institute of Geophysics at Polish Academy of Sciences found similar findings by analyzing oxygen isotopes from Antarctic rocks. The paper’s authors dated the emergence of freshwater to at least 3.7 billion years ago. Though the date is later than Gamaleldien’s work suggested, it still substantiates that freshwater may have been on the planet earlier than the previously theorized date of 3.5 billion years ago.
Now, with the potential for life five hundred million years earlier than previously thought, Gamaleldien, who has moved to Khalifa University in the United Arab Emirates, hopes to shift his focus to finding proof of life through RNA chemical traces from rocks. “We should push scientists and astrobiologists to start to search for new life,” Gamaleldien said.