Seismologists have discovered that a mysterious layer of quartz crystals around the Earth’s core is caused by water reaching depths
Have you ever wondered if seawater escapes through cracks in the Earth’s crust? The surprising answer is: Yes, and that it penetrates very deep, into the interior of the earth.
A few decades ago, seismologists studying the depths of the planet discovered a thin layer a few hundred kilometers thick. The origin of this layer, known as the E primary layer, has been a mystery until now.
An international team of geoscientists, including scientists at Arizona State University, have found that water from Earth’s surface can penetrate deep into the planet, changing the composition of the outermost region of the liquid metal core and forming a thin, distinct layer. Her research was recently published in Nature Geoscience.
Research shows that surface water was transported deep into the Earth over billions of years by the sinking or subduction of tectonic plates. When it reaches the core-mantle boundary, about 1,100 miles (1,800 kilometers) below the surface, this water triggers a profound chemical interaction that changes the structure of the core.
Together with Yong Jae Lee from Yonsei University (South Korea), American scientists have shown through high-pressure experiments that subducted water reacts chemically with nuclear materials. This reaction creates a hydrogen-rich, silicon-poor layer that transforms the outermost region of the core into a film-like structure. In addition, the reaction creates quartz crystals that rise and integrate into the mantle. This modified liquid metal layer is expected to be less dense and have lower seismic velocities, consistent with anomalous features mapped by seismologists.
“For years it was believed that the exchange of substances between the Earth’s core and mantle was low. However, our recent high-pressure experiments show a different story. We found that when water reaches the core-cladding boundary, it reacts with the silicon in the core to form silica,” explains Shim. “This discovery, together with our previous observation of diamond formation by the reaction of water with carbon in an iron fluid at extreme pressure, indicates a much more dynamic core-mantle interaction, suggesting an important material exchange.”
This finding expands our understanding of Earth’s internal processes and suggests a more extensive global water cycle than previously thought. The altered core film has profound effects on the geochemical cycles that connect the surface water cycle to the deep metallic core.
For this study, geoscientists used advanced experimental techniques at the Advanced Photon Source at Argonne National Laboratory and at PETRA III at the German Electron Synchrotron in Germany to reproduce the extreme conditions of the core-mantle boundary.
A hydrogen-enriched layer in the uppermost outer core, derived from deeply subducted water