HONOLULU, Nov. 13 (UPI) -- Researchers say at least some of the water on Earth today has been here the whole time, hiding deep beneath the planet's crust.
The water was found inside ancient volcanic glass sourced from rocks on Baffin Island in Canada. The discovery suggests Earth was formed in part by water-soaked dust particles. Much of that water was certainly lost over time -- early Earth was too hot to hold water on its surface -- but some of it remained trapped.
"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," Lydia Hallis, a researcher at the University of Hawaii at Manoa, explained in a press release.
Inside the rocks, researchers found water. They were able to tell they were ancient water molecules by measuring the ratio of hydrogen to deuterium.
Deuterium is a hydrogen isotope with an atomic mass of two. Within its core lies a proton and a neutron. Plain hydrogen has an atomic mass of one -- just one proton. In the wake of the big bang, a baseline ratio of hydrogen to deuterium was locked in place. But that ratio can by altered by space's varied conditions.
Solar storms can steal away hydrogen from the atmosphere, and comet impacts can deliver extra deuterium. Watery dust sealed up in the rocks of early Earth would be unaffected by such processes, leaving their ratio much the same.
And that's what researchers found.
"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," Hallis said. "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."
Hallis and her colleagues detailed their discovery in a new paper, published this week in the journal Science.
"It's an exciting discovery, and one which we simply didn't have the technology to make just a few years ago," Hallis added. "We're looking forward to further research in this area in the future."
Part of that future research may involve testing the ratio of hydrogen to deuterium on Mars, another planet that may have inherited some of its ancient water from protoplanetary dust.