New research suggests that the mysterious D’ layer at the boundary between Earth’s core and mantle may have formed from the remnants of an early giant impact, and that iron-rich peroxide plays a key role in its unique and long-lived properties.

Deep within the Earth lies a mysterious layer called the D layer. Located about 3,000 kilometers below, this region lies just above the boundary between the planet’s molten outer core and its solid mantle. Unlike a perfect sphere, the D” layer is surprisingly irregular. Its thickness varies greatly from one place to another; In some areas, there is no D layer at all, similar to how continents rise above Earth’s oceans. These interesting variations have attracted the attention of geophysicists, who describe layer D as a heterogeneous or inhomogeneous region.

Dr. Qingyang Hu (Advanced Research Center for High Pressure Science and Technology) and Dr. A new study led by Jie Deng (Princeton University) suggests that the D” layer may date back to Earth’s earliest days. Their theory is based on the hypothesis of a giant impact, in which a Mars-sized object crashed into the proto-Earth, subsequently creating a planet-sized magma ocean. They believe the D” layer may be a unique composition left over from this massive impact and could potentially hold the keys to the formation of the Earth.

Water in magma ocean

Dr. Jie Deng emphasizes that there is a significant amount of water in this global magmatic ocean. The exact origin of this water remains a matter of debate, with various theories put forward, including its formation as a result of a reaction between nebular gas and magma or direct distribution from comets. Dr. Deng continues: “The general view is that water cooled and condensed at the bottom of the magma ocean. In the final stages, the magma closest to the core could contain amounts of water comparable to Earth’s modern oceans.”

Extreme pressure and temperature conditions at the bottom of the igneous ocean may have created a unique chemical environment that encouraged unexpected reactions between water and minerals. Dr. “Our study shows that this aqueous magmatic ocean contributes to the formation of an iron-rich phase called iron magnesium peroxide,” explains Qingyang Hu. This peroxide, with the formula (Fe, Mg)O2, has a stronger iron predominance compared to other major components expected in the lower mantle. “According to our calculations, its affinity for iron may have led to the deposition of iron-dominated peroxide in layers several to tens of kilometers thick.

The presence of this iron-rich peroxide phase would alter the mineral composition of the D layer, deviating from our current understanding. According to the new model, a new group will dominate in D” minerals: weak silicate, iron-rich (Fe, Mg) peroxide and iron-poor (Fe, Mg) oxide. This iron-dominated peroxide also has low seismic velocities and high electrical conductivity, making it a potential candidate for explaining Layer D’s unique geophysical properties. These features include ultra-low velocity zones and high conductivity layers that contribute to well-healing. Known compositional heterogeneity of layer D.

“Our findings suggest that iron-rich peroxide formed from ancient waters in the magmatic ocean played a crucial role in the formation of heterogeneous structures of the D layer,” Qinyang said. said. The strong affinity of this peroxide for iron creates a sharp contrast in density between these iron-rich spots and the surrounding mantle. Essentially, it acts as an insulator, preventing their mixing and potentially explaining the long-term heterogeneity seen at the base of the lower mantle. Jie added: “This model is in good agreement with recent numerical simulation results and suggests that the heterogeneity of the lower mantle may be a long-lived feature.”