Water covers over two-thirds of Earth’s surface, but where it came from and when it arrived has long been debated. Many scientists have argued Earth formed as a dry planet, and then gained water millions of years later through the impact of water-bearing asteroids or comets. Now, it seems researchers from the University of Hawai’i at Mānoa have the answer.
The researchers, with the help of advanced ion microprobe instrumentation, have found that lava samples from Baffin Island in Canada contain evidence that Earth’s water has been around since Earth formed.
Earth formed around 4.6 billion years ago, after countless collisions of dust and rocks around the Sun. Dr. Lydia Hallis, a cosmochemist, and her team questioned if the ancient minerals that sit 1,800 miles (2,900 kilometers) deep in Earth’s mantle could hold the planet’s first water molecules.
By using the ion microprobe, researchers were able to focus on the minute pockets of glass inside these rocks, and thus were able to detect the tiny amounts of water. The ratio of hydrogen to deuterium in the water provided the researchers with valuable new clues as to its origins.
Hydrogen has an atomic mass of one, while deuterium, an isotope of hydrogen that is known as “heavy hydrogen,” has an atomic mass of two. Scientists have discovered that water from different types of planetary bodies in our solar system have distinct hydrogen to deuterium ratios, according to the University of Hawai’i.
“The Baffin Island rocks were collected back in 1985, and scientists have had a lot of time to analyze them in the intervening years. As a result of their efforts, we know that they contain a component from Earth’s deep mantle,” Dr. Hallis explained in a press release.
“On their way to the surface, these rocks were never affected by sedimentary input from crustal rocks, and previous research shows their source region has remained untouched since Earth’s formation.
Essentially, they are some of the most primitive rocks we’ve ever found on Earth’s surface,
and so the water they contain gives us an invaluable insight into Earth’s early history and where its water came from.
“We found that the water had very little deuterium, which strongly suggests that it was not carried to Earth after it had formed and cooled. Instead, water molecules were likely carried on the dust that existed in a disk around our Sun before the planets formed. Over time, this water-rich dust was slowly drawn together to form our planet.
“Even though a good deal of water would have been lost at the surface through evaporation in the heat of the formation process, enough survived to form the world’s water. It’s an exciting discovery, and one which we simply didn’t have the technology to make just a few years ago.
We’re looking forward to further research in this area in the future.”
Recent theoretical studies have found that some water molecules could have clung tightly to the coalescing dust particles even in the hot conditions of Earth’s formation, but Hallis’s study is the first to provide firm factual evidence, according to New Scientist.
Some room for doubt remains because of the mixing in Hallis’s ancient inclusions, Horst Marschall, a geoscientist at Woods Hole Oceanographic Institution in Massachusetts, told New Scientists.
But if Hallis is correct, then other planets in our solar system and elsewhere in the galaxy are likely to have formed with water present from the beginning.
“That would make habitable worlds much more likely,” says Marschall.
“This changes everything,” Steve Desch, an astrophysicist and professor in the School of Earth and Space Exploration at Arizona State University, who was not involved in the study, told Live Science.
“The debate about the origins of Earth’s water has centered for decades on whether Earth got its water from comets or chondrites (rocky meteorites),” he said. With this study suggesting that dust and gas around the Sun were important contributors as well, it calls for a re-evaluation of earlier conclusions that overlooked the role of material within the so-called solar nebula.
Hallis said with her results it could mean that water-rich planets like Earth are not so rare after all. The results were published in Science, titled “Evidence for primordial water in Earth’s deep mantle.”
Additional samples could shed more light on primordial water, Hallis said. “I would really like to go to Baffin Island to collect more samples; I think it would be a really good field expedition.”