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| IMAGE CREDITS: DEERHEARTE SHAMANIC |
An international team of scientists have decoded one
of those messages, which came in the form of high-pressure
ice crystals present in diamonds. Perhaps confusingly, this ice is a
sign of liquid water from deep in the mantle. These diamonds could help
researchers understand just how much water hides beneath our planet’s crust.
“One essential question that we are working on is
how much water is actually stored in the mantle. Is it oceans, or just a little
bit?” study first author Oliver Tschauner from the University of Nevada, Las
Vegas told Gizmodo. “This work shows there can be free excess fluids in the
mantle, which is important.”
The upper layer has a little
bit of water, but scientist estimate 10 times more water may be in the
transition zone, where minerals seem to be more soluble. The lower
layer’s minerals don’t seem to hold water as well. There’s already evidence of
water in the mantle in different forms, such as water that has been broken up
and incorporated into other minerals. But these diamonds contain water frozen
into a special kind of ice crystal, called ice-VII. There are lots of different
ways water can crystallize into ice, but ice-VII is formed under higher
pressures.
Essentially, while the diamond was forming, it must
have encapsulated some liquid water from around the transition zone. The high
temperatures prevented this water from crystalizing under the high pressures.
As geologic activity moved the diamonds to the surface, they maintained the
high pressures in their rigid crystal structures—but the temperature dropped.
This would have caused the water to freeze into ice-VII.
Panero, who was not involved in this study, again
stressed that this isn’t the first evidence of fluid water in the mantle. Study
author Tschauner pointed out that others have found diamonds with chemically
bound water—but this, instead, is free water that’s frozen into ice. Panero
also reminded me that the Earth’s mantle is solid, but this offers evidence of
fluid flowing around inside the transition zone.
Among other things, the varying composition of
materials at different layers of the mantle can affect where and how well
tectonic slabs that have sunk back into Earth’s interior melt and release their
minerals, Tschauner and his team contend. For instance, the density and
viscosity of Earth’s interior affect the level at which sinking slabs reach
neutral buoyancy, thus stalling their descent.
That, in turn, influences where
the slabs melt and release the water and other minerals they hold. Overall, the
team’s new findings may lead to more accurate models of what’s going on at
different depths deep within Earth
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