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UH team sheds light on origin of Earth’s water

  • COURTESY LYDIA J. HALLIS
    These are scanning electron microscope images of a type of basaltic rock called picrite
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University of Hawaii researchers who examined some of Earth’s most primitive rocks have found that they contain droplets of water — evidence that water was part of the planet’s formation.

Scientists have long been uncertain whether water was present from the beginning or if it arrived later, perhaps on comets and meteorites.

Now UH researchers, using advanced instrumentation, have found that rocks from Baffin Island in Canada contain primordial water. Their research was published in the Nov. 13 issue of the journal Science.

"Water molecules were likely carried on the dust that existed in a disk around our sun before the planets formed," said Lydia Hallis, a Marie Curie Research Fellow atthe University of Glasgow, Scotland, and a former postdoctoral fellow at the UH NASA Astrobiology Institute. "Over time this water-rich dust was slowly drawntogether 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, enoughsurvived to form the world’s water."

The UH team, which included Gary Huss, Kazuhide Nagashima, Jeff Taylor, Mike Mottl, and Karen Meech, examined rocks collected in 1985 at Baffin Island, north ofNewfoundland. The rocks originated in the Earth’s deep mantle.

"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 remaineduntouched since Earth’s formation," Hallis said in a UH release last week. "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."

Key to the findings is the ratio of hydrogen in the water to an isotope, deuterium or "heavy hydrogen." Scientists have discovered that water from different types ofplanetary bodies in the solar system have distinct hydrogen-to-deuterium ratios.

The droplets were examined with an instrument called an ion microprobe.

"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.

She called the discovery "exciting" and "one which we simply didn’t have the technology to make just a few years ago."

The research was funded by the UH NASA Astrobiology Institute.

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