Seismologists studying the deep planet a few decades ago discovered a thin
layer that was hardly more than a few hundred kilometers thick. Until
recently, the origin of this layer—also referred to as the E prime layer—was
unknown.
Researchers from Arizona State University, Dan Shim, Taehyun Kim, and
Joseph O'Rourke of the School of Earth and Space Exploration, are part of an
international team that has discovered that water from the Earth's surface
can seep deeply into the planet, changing the makeup of the metallic liquid
core's outermost region and forming a distinct, thin layer. An illustration
showing how a chemical reaction triggered by water causes silica crystals to
emerge from the liquid metal of the Earth's outer core.
Nature Geoscience
published
their study article.
Studies show that subducted, or falling, tectonic plates have carried
surface water deep into the Earth over billions of years. This water causes
a significant chemical reaction that modifies the structure of the core when
it reaches the core-mantle border, which is located around 1,800 miles below
the surface.
Shim and his colleagues have shown through high-pressure studies that
subducted water chemically interacts with core materials, working with Yong
Jae Lee of Yonsei University in South Korea. This reaction changes the
outermost outer core area into a film-like structure and creates a layer
that is silicon-depleted and rich in hydrogen. The process also produces
silica crystals that ascend to the surface and incorporate into the
mantle.
Seismologists have identified abnormal properties, such as lower seismic
velocities and less density in this modified liquid metallic layer.
It has long been thought that there is little material exchange between the
Earth's core and mantle. However, our latest high-pressure tests tell a
different tale. We discovered that water interacts with silicon in the core
at the core-mantle border to generate silica "explained Shim.
"This discovery, along with our previous observation of diamonds forming
from water reacting with carbon in iron liquid under extreme pressure,
points to a far more dynamic core-mantle interaction, suggesting substantial
material exchange."
This discovery contributes to our knowledge of Earth's interior dynamics by
pointing to a larger global water cycle than previously thought. The
modified "film" of the core has significant effects on the geochemical
processes linking the deep metallic core and the surface-water cycle.
In order to reproduce the harsh circumstances at the core-mantle boundary,
a worldwide team of geoscientists used cutting-edge experimental techniques
at the Advanced Photon Source of Argonne National Lab and PETRA III of
Deutsches Elektronen-Synchrotron in Germany.
Provided by
Arizona State University
