Rare Ice-VII Found in Diamond Suggests that there is Water inside Earth’s Mantle
“Shine bright like a diamond” seems to become more than just a Rihanna song lyric, but the leitmotif of recent science news. Last week, we reported about an amazing discovery about a diamond: in a study published in the journal Nature, geochemist Graham Pearson and his colleagues reported that they analyzed a tiny diamond which contained calcium silicate perovskite – a mineral never seen before at Earth’s surface. As we were saying on this occasion, the deep-Earth mineral has the power to reveal even more mysteries about the center of the planet. In a twist worthy of Jules Verne and other science-fiction writers, the science news this week also emphasize a diamond. This one, however, carries not mysterious minerals, but ultra rare Ice-VII, or, in simpler terms, traces of water that comes from the deep core of the planet. Of course, the results are shocking for the scientific community. Nevertheless, let us see what this is all about.
An international team of scientists from the United States and Canada has discovered the first direct evidence that pockets of fluid water may exist as far as 500 miles (805 km) deep into the Earth’s mantle. The results are available in the journal Science. According to the report, the diamonds they studied, originating from China, South Africa, and Botswana, showed some impurities. In the jewelry world, impure or imperfect diamonds have little to no value, but for science they are priceless. The amazing thing is that the scientists were looking for something else completely when they began studying the diamonds. But instead of the carbon dioxide in diamonds they wanted to see, they accidentally stumbled upon the first-ever samples of naturally occurring ice-VII on Earth.
The rare Ice-VII, while not “alien”, it a bit strange, to be honest, as it is almost non-existent on Earth, while it might play an important role elsewhere in the solar system, according to the scientists. Now, in order to explain Ice-VII, think about the ice you drink in your beverages. That is Ice-I. Ice-VII is 1.5 times more dense than Ice-I, its oxygen atoms move into a cubic arrangement, and it remains stable even as pressure increases. In order to occur, it needs both low temperatures and high pressure exceeding 30,000 atmospheres. In other words, it is not likely that it can form on the Earth surface but it is highly unlikely it can occur inside the Earth’s mantle. Even if the mantle can put such pressures, it is also very hot down there for ice to even be an idea. And this is where diamonds come into the story.
According to Oliver Tschauner from the University of Nevada – one of the study’s authors – diamonds often pick up molecules during their formation deep in the Earth. We learned that last week when the Cullinan Mine in South Africa produced the calcium silicate perovskite diamond. However, what jewelers call inclusions are sometimes just water. The great thing about diamonds, from this point of view, is that they keep their internal structures intact even when they leave the high-pressure mantle. In other words, the water in a diamond remains compressed, even if, technically, it is a liquid.
The ice natural diamonds sourced from between 255 and 410 miles (410-660 km) depth come from South Africa (Namaqualand), Botswana (Orapa), China (Shandong), Zaire, and Sierra Leone. This made the researchers conclude that “this is a global phenomenon.” Since the diamonds were born in the mantle under temperatures reaching more than 1,000 degrees Fahrenheit (538 degrees Celsius), it means that the mantle is made of silicate minerals (containing iron, calcium, aluminum, calcium silicate perovskite, ringwoodite and more) and now, we can clearly include water on the list.
According to the researchers, “These discoveries are important in understanding that water-rich regions in the Earth’s interior can play a role in the global water budget and the movement of heat-generating radioactive elements. They can help us create new, more accurate models of what’s going on inside the Earth, specifically how and where heat is generated under the Earth’s crust. In other words: it’s another piece of the puzzle in understanding how our planet works.”
While it is redundant from our part, in the light of these discoveries, we cannot help but emphasize on the importance of the Jules Vernesque journey to the core of the Earth, a Japanese scientific drilling project which may begin by 2030. We cannot wait to see what scientists will find deep down there, besides rare Ice-VII and other wonders hidden inside diamonds!
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