New research clarifies how water from Earth's surface can reach deep into the planet, leading to changes in the outermost area of the metallic liquid core. This discovery explains a previously mysterious thin layer within the Earth that has puzzled geologists for decades.
Unveiling the Mystery of E Prime Layer
Throughout billions of years, Earth's tectonic plates have been shuttling water downward through subduction zones, where they grind and slide beneath one another. Upon reaching the core-mantle boundary, located about 2,900 kilometers beneath the surface, this water triggers a potent chemical interaction.
A collaborative effort involving researchers from South Korea, the United States, and Germany conducted high-pressure experiments, revealing that this interaction results in the formation of a hydrogen-enriched top core layer and the transportation of silica to the lower mantle.
The layer, known as the E prime layer, was identified by seismologists imaging the deep planet a few decades ago. Scientists unveil the findings of the study, titled "A hydrogen-enriched layer in the topmost outer core sourced from deeply subducted water" published in the journal Nature Geoscience, unveiling the role of surface water in altering the composition of the metallic liquid core.
This discovery challenges the prevailing belief that material exchange between Earth's core and mantle is minimal. Contrary to this notion, the team's experiments demonstrated that when water reaches the core-mantle boundary, it reacts with silicon in the core, giving rise to silica.
The implications of understanding these dynamics are profound, particularly in comprehending the role of Earth's inner workings, especially the outer core's composition of iron and nickel, crucial for generating the planet's magnetic field, protecting life from solar winds and radiation.
The Earth's core-mantle boundary undergoes a sharp transition from silicate to metal, and the chemical processes taking place in this region have remained largely unexplored. The recent findings suggest that the enduring chemical exchange between the core and mantle, facilitated by the deep transportation of water over immense periods, could contribute to the formation of this enigmatic layer.
Density Variations and Hydrogen-Rich Layers
Density variations, believed to be due to different concentrations of light elements such as hydrogen or silicon, hint at a less dense and slower seismic-speed liquid metallic layer, as identified by seismologists.
However, reconciling seismic observations with the dynamic stability of the E prime layer becomes challenging, given that increasing the concentration of a single light element typically results in higher speed and lower density.
To explore potential explanations, the research team employed laser-heated diamond-anvil cells to replicate the conditions at the core-mantle boundary. Their experiments revealed that water, subducted into Earth's core, undergoes a chemical reaction with core materials, transforming the outer core into a hydrogen-rich film and dispersing silica crystals that ascend and integrate into the mantle.
This resulting layer of hydrogen-rich, silicon-poor material at the core's top exhibits reduced density and speed, aligning with observed seismic wave patterns.
Beyond impacting the deep water cycle, this modified core film suggests a more intricate global water cycle than previously understood. The researchers emphasize that this discovery, combined with their earlier observation of diamonds forming from water reacting with carbon under extreme pressure, points to a more dynamic core-mantle interaction, indicating substantial material exchange.
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