After decades of theorizing and searching,
scientists are reporting that they’ve finally found a massive reservoir
of water in the Earth’s mantle — a reservoir so vast that could fill the
Earth’s oceans three times over. This discovery suggests that Earth’s
surface water actually came from within, as part of a “whole-Earth water
cycle,” rather than the prevailing theory of icy cometsstriking
Earth billions of years ago. As always, the more we understand about
how the Earth formed, and how its multitude of interior layers continue
to function, the more accurately we can predict the future. Weather, sea
levels, climate change — these are all closely linked to the tectonic
activity that endlessly churns away beneath our feet.
This new study, authored by a range of geophysicists and scientists from across the US, leveragesdata
from the USArray — an array of
hundreds of seismographs located throughout the US that are constantly
listening to movements in the Earth’s mantle and core. After listening
for a few years, and carrying out lots of complex calculations, the
researchers believe that they’ve found a huge reserve of water that’s
located in thetransition zone between the upper and lower mantle — a region that occupies between 400 and 660 kilometers (250-410 miles) below our feet. [DOI: 10.1126/science.1253358 – “Dehydration melting at the top of the lower mantle”
As you can imagine, things are a little complex that
far down. We’re not talking about some kind of water reserve that can
be reached in the same way as an oil well. The deepest a human borehole has ever gone is just 12km
— about half way through the Earth’s crust — and we had to stop because
geothermal energy was melting the drill bit. 660 kilometers is a long,
long way down, and weird stuff happens down there.
Basically, the new theory is that the Earth’s
mantle is full of a mineral called ringwoodite. We know from experiments
here on the surface that, under extreme pressure, ringwoodite can trap
water. Measurements made by the USArray indicate that as convection
pushes ringwoodite deeper into
the mantle, the increase in pressure forces the trapped water out (a
process known asdehydration melting). That seems to be the extent of the
study’s findings. Now they need to try and link together deep-Earth
geology with what actually happens on the surface. The Earth is an
immensely complex machine that
generally moves at a very, very slow pace. It takes years of
measurements to get anything even approaching useful data. [Read: Is earthquake prediction finally a reality?]
With all that said, there could be massive repercussions if this study’s findings are accurate. Even if the ringwoodite only contains
around 2.6% water, the volume of the transition zone means this
underground reservoir could contain enough water to re-fill our oceans
three times over…..
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