Study Shines New Light on Source of Earth’s Water

by johnsmith

A new study in the journal Science suggests that water-soaked grains of dust present early in the Solar System are the source of Earth’s water.

Early Earth. Image credit: Christine Daniloff.

Early Earth. Image credit: Christine Daniloff.

Researchers have long been uncertain whether water was present at the formation of Earth, or if it arrived later, perhaps carried by comets or meteorites.

Now, a team of scientists has found that rocks from Baffin Island in Canada contain evidence that Earth’s water was a part of our planet from the beginning.

“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,” said Dr Lydia Hallis, a scientist at the University of Glasgow in Scotland and the lead author on the study.

Scientists can learn about the origins of water on a planet by studying the water’s deuterium/hydrogen (D/H) ratio.

Different factors, like tectonic mixing, can affect this ratio over time. Only areas deep within Earth that have not been affected by these processes are likely to preserve Earth’s initial D/H ratio.

Deep lava flows that churned up basalt from the mantle to the surface of Baffin Island provided the team with relatively unaltered samples.

“On their way to the surface, these rocks were never affected by sedimentary input from crustal rocks,” Dr Hallis explained.

“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.”

Analysis of the basalt’s D/H ratio revealed lower amounts of deuterium than found in previous studies, providing a new baseline for Earth’s original D/H signature.

“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,” Dr 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.”

“It’s an exciting discovery. We’re looking forward to further research in this area in the future,” Dr Hallis said.


Lydia J. Hallis et al. 2015. Evidence for primordial water in Earth’s deep mantle. Science, vol. 350, no. 6262, pp. 795-797; doi: 10.1126/science.aac4834

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