Interaction with the Earth’s core
Decades ago seismologists identified a thin, enigmatic layer just over a few hundred kilometers thick near the planet’s deepest interior. The origin of this primary layer E remained a mystery, yet new research has brought surprising clarity. An international team, including scientists from Arizona State University such as Dan Shim Taehyun Kim and Joseph O’Rourke from the School of Earth and Space Exploration, has shown that water present at Earths surface can travel to surprising depths. It can penetrate into the outer core and alter its composition, forming a distinct and delicate film at the top of the core. The team reports these findings as part of a broader exploration of how surface water may be transported to extreme depths through subduction and long geological timescales. These results were detailed in an issue of Natural Geology and are interpreted as evidence that surface water travels down through the mantle along descending tectonic plates and accumulates in the deep Earth.
Through high pressure experiments that involved collaboration with Yong Jae Lee of Yonsei University in South Korea, the researchers demonstrated that water chemically reacts with core materials when it reaches the core mantle boundary around 2900 kilometers beneath the surface. The reaction forms a hydrogen rich, silicon poor layer that behaves like a film within the upper outer core. In the same process, silica crystals are generated and rise toward the mantle. This creates a shift in the density and seismic velocity of the region, consistent with long observed anomalies mapped by seismologists.
According to the study authors, the exchange of material between the core and mantle is more substantial than once believed. The interaction between water and core silicon leads to silica formation when water encounters the core mantle boundary, a finding that revises earlier assumptions about a constrained exchange at these depths. This insight is echoed by the authors who note that diamonds can also form when water reacts with carbon in liquid iron under extreme pressure, pointing to a much more dynamic core mantle interaction than previously thought and indicating significant material exchange between layers.
The discovery sheds light on Earths internal processes and reveals a broader, more interconnected global water cycle that connects surface waters to the deep metallic core. The altered film within the outer core could influence geochemical cycles that link shallow water processes with deep Earth dynamics. This work was conducted by an international team of geoscientists using advanced experimental techniques at the Advanced Photon Source at Argonne National Laboratory and at PETRA III at the Deutsches Elektronen-Synchrotron in Germany, enabling the replication of extreme core mantle boundary conditions. These findings contribute to a more nuanced understanding of how water and materials move through Earths interior over geological timescales. The study is reported in Nature Geology and is part of a growing body of work examining deep Earth chemistry and dynamics. Attribution: Nature Geology 2023
This research enhances the understanding of the deep water cycle and the interconnected nature of Earths interior. It shows how surface processes, subduction zones, and deep Earth chemistry combine to shape the structure of the core mantle boundary. The research emphasizes that the Earth is a dynamic system where movement of water and other elements at great depths can alter seismic properties and influence geochemical cycles that reach from the surface to the heart of the planet. The results invite further studies to map how widespread this water driven interaction is and what it means for models of planetary differentiation and mantle convection. Attribution: Nature Geology 2023
In summary, the collaboration reveals a revised picture of Earths interior in which water, delivered via deep subduction, can reach the core mantle boundary, react with core materials, and create a differentiated film that changes the physical and chemical state of the upper outer core. This film interacts with silicon to form silica and can alter density and seismic velocities, aligning with long standing seismic observations. The implications extend to our understanding of global geochemical cycles and the deep Earth water inventory, offering a more integrated view of how surface water connects to deep planetary processes. Attribution: Nature Geology 2023
Reference work: a study published in Nature Geology discussed the transport of surface water to Earth’s deepest depths through subduction and high pressure experiments. Attribution: Nature Geology 2023