Earth’s water may have come from within, not meteorites – UCD

3 Feb 201711 Shares

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Quartz. Image: Bostock/Shutterstock

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Water might not have come from meteorites crashing into Earth and depositing ice, as a new study suggests that silicon and nitrogen reactions may have been the source instead.

While the hunt for water elsewhere in our solar system rumbles on – Mars, Jupiter moons and comets each the home to incredible discoveries in recent years – the source of Earth’s water has remained a relative mystery.

One school of thought is that meteorites crashed into Earth over millions and millions of years, depositing substances that held ice, as well as water-giving qualities, as they made impact.

Earth

Earth does it all

However, scientists at UCD have suggested a different scenario. Their research shows that reactions between high-pressure and high-temperature fluid hydrogen and silicon dioxide in quartz, found in Earth’s upper mantle, can form liquid water under the right conditions.

Those right conditions include temperatures of just over 1,400 degrees Celsius, with pressure 20,000 times higher than Earth’s atmospheric pressure. The right ingredients include silica, found in the quartz that is in abundance above and below the Earth’s mantle.

The scientists had expected that the water would form on the surface of the silica, but instead they were surprised to find that the water remained trapped inside the silica, leading to a massive build-up of pressure.

What’s interesting about this is the self-sufficient creation of pressure on the planet, in contrast to other suggestions relying on massive asteroid impacts to create temperature and force, leading to life.

For the crater good

Last year, Trinity College Dublin researchers studied the Sudbury Basin in Canada, finding that hydrothermal environments were created by hot, melting craters left by meteorite impacts.

If the craters were deep enough, with high enough walls, they could trap water inside, mix it with the minerals deposited by space rocks and cook it all up in the hot impact zone.

While this was not the genesis of water, the necessity for alien impacts is one theory that UCD’s Prof Niall English disputes.

“Vast amounts of water have been discovered in the Earth’s mantle in the last few years,” he told Siliconrepublic.com. “It’s not an opinion of whether it exists, that’s now a fact; it’s how and why.”

Bit of both?

English believes meteorites also deposited water on Earth over millions and millions of years, across countless impacts, but he estimates that only a small percentage of our water originated in this way.

The vast majority came from naturally occurring chemical reactions, and Earth’s own “self-contained” pressure generation, he said.

“We were initially surprised to see in-rock reactions, but we then realised that we had explained the puzzling mechanism at the base of earlier Japanese experimental work finding water formation,” said English.

“We concluded that these findings help to rationalise, in vivid detail, the in-mantle genesis of water. This is very exciting and in accord with very recent findings of … water in the Earth’s mantle.”

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Gordon Hunt is a journalist at Siliconrepublic.com

editorial@siliconrepublic.com