Oceans' Worth of Water Hidden Deep in Earth, Ultra Rare Diamond Suggests

A beautiful blue flaw in a gem-quality diamond from Botswana is actually a tiny fragment of Earth's deep interior -- and it suggests our planet's mantle contains oceans' worth of water. Scientific American: The flaw, technically called an inclusion, looks like a fish eye: a deep blue center surrounded by a white haze. But it's really a pocket of the mineral ringwoodite from 660 kilometers down, at the boundary between the upper and lower mantle. This is just the second time scientists have found this mineral in a chunk of crystal from this zone, and the sample is the only one of its kind currently known to science. The last example was destroyed during an attempt to analyze its chemistry. [...] The discovery indicates that this very deep zone of Earth is soggy, with vast amounts of water locked up tight within the minerals there. Though this water is chemically bound to the minerals' structure and doesn't flow around like an actual ocean, it does likely play an important role in how the mantle melts. This in turn affects big-picture geology, such as plate tectonics and volcanic activity. For example, water could contribute to the development of areas of mantle upwelling known as plumes, which are hotspots for volcanoes. The stunning bit of diamond-encased mantle was discovered by Tingting Gu, a mineral physicist now at Purdue University, who was at the time doing research at the Gemological Institute of America. Her job was to study rare inclusions found in diamonds. Inclusions are undesirable for jewelry because they cloud a diamond's sparkle. But they're often interesting to scientists because they trap bits of the environment where the diamond formed millennia earlier. The vast majority of diamonds form between about 150 to 200 km below Earth's surface. But a handful come from much deeper. It is often difficult to pinpoint exactly how deep, but the new sample was remarkably accommodating on that front, Gu and her colleagues reported on Monday in a study published in Nature Geoscience. Ringwoodite can only form at incredibly high pressures. It is not found in Earth's crust, but it is sometimes seen trapped in meteorites that underwent major cosmic trauma. In Earth's mantle, ringwoodite exists at the pressures present down to 660 km.

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