Magazine article Science News

Water Permeates Earth's Interior: Blue Mineral Offers Peek at Conditions Inside the Mantle

Magazine article Science News

Water Permeates Earth's Interior: Blue Mineral Offers Peek at Conditions Inside the Mantle

Article excerpt

An ocean's worth of water is locked deep within the Earth and may influence all sorts of geological processes, including the grinding of tectonic plates, the formation of volcanoes and the movement of chemical elements.

Researchers examined the rumbling of seismic waves and performed lab experiments that mimicked the crushing pressures and extreme temperatures of Earth's mantle, the thick layer of the planet between the crust and core. The results make a strong case that a huge amount of water resides within the planet, says Yale University geophysicist Jennifer Girard, who was not involved with the study. The findings appear in the June 13 Science.

Some water may have been trapped during the early days of Earth's history, before oceans formed. Water also travels into the mantle during subduction, when tectonic plates collide and ocean-soaked crust dives deep into the mantle. That water probably influences the flow of material in Earth's innards, but exactly where it goes hasn't been clear.

Many geologists think that the water gets trapped about 410 to 660 kilometers beneath Earth's surface, where the upper mantle transitions into the partially molten lower mantle. But evidence has been scant. Holes dug from the surface merely penetrate Earth's crust, so scientists have relied on indirect evidence, including bits of rock ejected by volcanoes, to get a sense of what's happening deeper down.

A recent analysis of a battered diamond that made the 400-kilometer trek from mantle to surface in an estimated 10 hours revealed a tiny bit of the sapphire-blue mineral ringwoodite--a mineral that's especially good at holding water in the form of hydroxide ions. Ringwoodite is a form of the mineral olivine, which is common in shallow parts of the mantle. Scientists think ringwoodite predominates in the higher-pressure environment of the mantle's transition zone. …

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