by Andy Coghlan
23 November 2016
from NewScientist Website
Earth's mantle may contain many oceans' worth of water - with the deepest 1000 kilometers down.
This water is much deeper
than any seen before, at a third of the way to the edge of Earth's
core. Its presence was indicated by a diamond spat out 90 million
years ago by a volcano near the São Luíz river in Juina, Brazil.
When the researchers took
a closer look at it with infrared microscopy, they saw unmistakable
evidence of the presence of hydroxyl ions, which normally come from
water. They were everywhere, says Jacobsen.
It is made of a ferropericlase mineral, which is composed of iron and magnesium oxide, and can also absorb other metals such as chromium, aluminium and titanium at ultra-high temperatures and pressures typical of the lower mantle.
"This water is much deeper
than ever found before,
at a third of the way
to the edge of Earth's core"
Steve Jacobsen found that these additional metals had separated from the ferropericlase - something that happens in the milder conditions a diamond experiences as it edges up through shallower depths.
But for the metals to be present at all, the diamond must have originated in the intense conditions of the lower mantle (Evidence for H²O-bearing fluids in the lower mantle from diamond inclusion).
The clincher is that as the inclusion was trapped in the diamond the whole time, the water signature can only have come from the diamond's place of formation in the lower mantle.
His team has previously found evidence of massive amounts of water some 600 kilometers down, mixed in with rock.
For example, it is
possible that Earth had water from day one in the very dust and
rocks that first formed it.
Jacobsen thinks that this water may help explain why Earth is the only planet we know to have plate tectonics.
The hope is that such research will yield insights into how our oceans and atmosphere formed in the first place.