Rare mineral fragment points scientists to vast repository of underground water

Thanks to a tiny fragment of a mineral that, up until now, has only been found in meteorites, scientists have their first hard evidence that there are vast amounts of water deep down in the Earth's crust.

This discovery came when John McNeill, a graduate student at the University of Alberta at the time, was examining a small, nondescript chunk of brown diamond for specific kinds of minerals. This diamond originated deep inside the Earth, and was brought to the surface long ago by a volcanic eruption, trapped inside a type of rock known as kimberlite. It was eventually fished out of a riverbed in west-central Brazil, and made its way to the laboratory of McNeill's graduate supervisor, Professor Graham Pearson, who's work with these deep-Earth diamonds can tell a lot about the conditions where this diamond formed by looking at what's inside them. McNeill didn't find the minerals he was originally searching for, but he happened upon something else that was more surprising — a tiny fragment of a mineral known as ringwoodite.

Ringwoodite forms when olivine, one of the most common minerals in the Earth, is put under extremely high pressures. It's been found in meteorites before, where it was produced during impacts — either when the rock was still flying around in space or when it quite abruptly found itself on the surface of Earth. Scientists have also figured that it can form and stay stable deep in the Earth as well, in the transition zone between the upper and lower mantel. It's just that there's been no way, as of yet, to venture down that deep to actually find samples of it.

So, this was apparently the very first time that anyone had found a physical sample of ringwoodite that originated from inside the Earth.

"It's so small, this inclusion, it's extremely difficult to find, never mind work on," Pearson said in a University of Alberta news release, "so it was a bit of a piece of luck, this discovery, as are many scientific discoveries."

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However, this sample was also remarkable in another way.

Analyzing the ringwoodite showed that roughly 1.5 per cent of its weight was water, locked away in the mineral at the time it was formed, a bit like a time capsule. That may not seem like a lot, but when you add up the total volume of the transition zone, even that small per cent of that comes out to be a lot of water. Scientists had speculated that the transition zone could hold an abundance of water, but until now, there had been no hard evidence to confirm it.

"This sample really provides extremely strong confirmation that there are local wet spots deep in the Earth in this area," said Pearson, according to the news release. "That particular zone in the Earth, the transition zone, might have as much water as all the world's oceans put together."

This not only confirms about half a century of theoretical work by scientists, but it also seems to count as yet another prediction of Jules Verne's that eventually came true. He wrote about a vast underground ocean in Journey to the Center of the Earth, and while this isn't exactly what he envisioned, I'd say it probably still counts. So 'well done' to the scientists involved in this study, and well done to M. Verne!

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