Beijing: Around 3,000 kilometers beneath Earth’s surface lies the enigmatic D” layer, a band of material that has puzzled scientists for decades due to its irregular composition. Recent research suggests this layer may have originated from an ancient magma ocean that once enveloped early Earth billions of years ago.
An international team of researchers, through advanced simulations, proposes that extreme pressures and temperatures at the bottom of this primordial magma ocean induced chemical reactions that created the D” layer’s lumpy structure. Unlike previous models, these simulations incorporated the significant role of water present in ancient magma oceans.
The study, published in National Science Review, posits that water mixed with minerals to form iron-magnesium peroxide ((Fe,Mg)O2), which attracted iron and led to the formation of iron-rich layers where the D” layer is located, just above the boundary between Earth’s molten outer core and the surrounding mantle.
Key Findings
•”Our research suggests this hydrous magma ocean favored the formation of an iron-rich phase called iron-magnesium peroxide,” explained Qingyang Hu, a data scientist at the Center for High Pressure Science and Technology Advanced Research (HPSTAR) in Beijing. This phase accumulated in layers several to tens of kilometers thick.
•As iron was dragged around within the magma ocean, chemical reactions became concentrated in specific areas, forming the D” layer. This could also elucidate the existence of ultra-low velocity zones (ULVZs) deep inside Earth, where seismic waves significantly slow down.
•The iron-rich layers likely had an insulating effect, maintaining distinct regions at the base of the lower mantle, further contributing to the D” layer’s heterogeneity.
The study’s insights align with the hypothesis that a massive collision with another planet about 4.5 billion years ago created this ancient magma ocean. This cataclysmic event not only led to the formation of the Moon but also left behind a mix of volatile elements crucial for life on Earth.
Implications for Earth’s History
Understanding the D” layer’s formation provides valuable clues about Earth’s early conditions. “This model aligns well with recent numerical modeling results, suggesting the lowermost mantle’s heterogeneity may be a long-lived feature,” said Jie Deng, a geophysicist from Princeton University.
As scientists delve deeper into Earth’s geological history, studies like this help reconstruct the planet’s formative years and improve our comprehension of its inner workings.
The research presents a significant step forward in unraveling the mysteries of Earth’s interior and offers a clearer picture of the dynamic processes that shaped our planet billions of years ago.
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