Scanning electron microscope image of a Baffin Island picrite (type of basaltic rock). The mineral olivine, shown as abundant mid-gray color cracked grains (A), hosts glassy melt inclusions (B) containing tiny amounts of water sourced from Earth’s deep mantle. (image by Lydia J. Hallis)

Water covers more than two-thirds of Earth’s surface, but its exact origins are still something of a mystery. Scientists have long been uncertain whether water was present at the formation of the planet, or if it arrived later, perhaps carried by comets and meteorites.

Now researchers from the University of Hawaiʻi at Mānoa, using advanced ion-microprobe instrumentation, have found that rocks from Baffin Island in Canada contain evidence that Earth’s water was a part of our planet from the beginning. Their research, “Evidence for primordial water in Earth’s deep mantle,” was published in the November 13 issue of the journal Science.

The research team was led by cosmochemist Lydia Hallis, then a postdoctoral fellow at the UH NASA Astrobiology Institute and now Marie Curie Research Fellow at the University of Glasgow, Scotland. The paper co-authors are Gary Huss, Kazuhide Nagashima, G. Jeffrey Taylor, Mike Mottl and Karen Meech.

Detecting tiny amounts of water

The ion microprobe allowed researchers to focus on minute pockets of glass inside these scientifically important rocks, and to detect the tiny amounts of water within. The ratio of hydrogen to deuterium in the water provided them with valuable new clues as to its origins.

Hydrogen has an atomic mass of one, while deuterium, an isotope of hydrogen also 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.

The Baffin Island rocks were collected in 1985 and scientists have had a lot of time to analyze them in the intervening years. “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,” said Hallis.

“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,” said Hallis. “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.”

For the full story, read the Institute for Astronomy news release.