Home' Trinidad and Tobago Guardian : March 16th 2014 Contents A38
Sunday Guardian www.guardian.co.tt March 16, 2014
This diamond has provided evidence of a "wet zone" deep inside the earth's
crust. The stone was found in 2008 by artisan miners working the Juína
riverbeds in Mato Grosso in western Brazil, and has recently been analysed by
geologists at the University of Alberta. PHOTO: UNIVERSITY OF ALBERTA
A small, battered diamond found in the gravel
strewn along a shallow riverbed in Brazil has pro-
vided evidence of a vast "wet zone" deep inside the
Earth that could hold as much water as all the
world s oceans put together.
The water is not sloshing around inside the planet,
but is held fast within minerals in what is known as
the Earth s transition zone, which stretches from 410
to 660 km (250--400 miles) beneath the surface.
"It s not a Jules Verne-style ocean you can sail a
boat on," said Graham Pearson, a geologist who
studied the stone at the University of Alberta. The
water-rich zone could transform scientists under-
standing of how some of the Earth s geological features
Tests on the diamond revealed that it contained
a water-rich mineral formed in the zone. Researchers
believe that the gemstone, which is oblong and about
five mm long, was blasted to the surface from a depth
of about 500 km by a volcanic eruption of molten
rock called kimberlite.
The battle-scarred gem has a delicate metallic
sheen, but is pitted and etched from its violent journey,
which probably took several days and ended with
the stone shooting up through the Earth s crust at
a speed of about 70 km/h (40 mph).
"It s a fairly ugly diamond. It looks like it s been
to hell and back," said Pearson, adding that the gem
was worth about US$20 at most. The stone was
found in 2008 by artisan miners working the Juína
riverbeds in Mato Grosso in western Brazil.
Most diamonds used in jewelry form at much shal-
lower depths, about 150 km down. Those that form
in the transition zone are called super-deep diamonds
and are distinguished by their battered appearance
and low nitrogen content.
Pearson and his team were testing the diamond
to find minerals they could use to work out its age.
But by chance they discovered a speck of mineral
called ringwoodite, a type of olivine that forms under
extremely high pressures. The mineral inclusion was
too small to see with the eye.
Without the diamond---and the water-rich mineral
inside it---scientists had no hope of confirming the
make-up of material so deep inside the Earth s interior.
"No one is ever going to run a geological field trip
to the transition zone 500 km beneath the Earth s
surface, and no one is ever going to drill down to
the transition zone," said Pearson. "It was a total
piece of luck that we found this."
For decades, scientists have suspected that ring-
woodite made up much of the deep Earth, because
olivine is so widespread underground. But no one
had ever found any ringwoodite from the Earth s
interior that proved the idea beyond doubt. In the
transition zone where the diamond and its ringwoodite
was formed, the pressure reaches 200,000 atmos-
Tests on the mineral found that about 1.5 per cent
of its weight is water. "That doesn t sound like much,
but when you calculate the vast volumes of ring-
woodite thought to exist in the deep Earth, the
amount of water might be as high as that contained
in all the world s oceans," Pearson told the Guardian.
That amounts to more than one billion billion tonnes
At the very least, the scientists say, there must be
local wet spots or "oases" in the Earth s interior.
"The beauty of this diamond is that it gives us a real
sample from those depths," Pearson said. The diamond
is described in the latest issue of the journal Nature.
A huge water store in the Earth s mantle might
help geologists explain some oddities seen on the
planet s surface. Water in the transition zone could
dissolve in molten magma and reach the undersides
of continental plates, where it would weaken the
Rough diamond hints
at water inside Earth
huge slabs of rock. That could create weak spots
prone to volcanoes, and even cause "uplift," where
the land rises up.
Hans Keppler, at the University of Bayreuth in
Germany, said: "Until now, nobody had ever seen
ringwoodite from the Earth s mantle, although geo-
physicists were sure that it must exist. Most people,
including me, never expected to see such a sample."
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