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  • Context (Phys): Deep within Earth, there lies a mysterious layer called the D” layer.

    Earth's D Layer - PMF IAS

    Credits: Spring8

  • Located roughly 3,000 kilometres down, this zone sits just above the boundary between the planet’s molten outer core and its solid mantle.
  • Theory relying on the Giant Impact hypothesis believes the D” layer may be a unique composition leftover from this colossal impact, potentially holding clues to Earth’s formation.
  • The giant Impact hypothesis proposes a Mars-sized object slammed into the proto-Earth, creating a planet-wide magma ocean in the aftermath.
  • The D” layer is not perfectly sphere and is surprisingly patchy. Its thickness varies greatly from place to place, with some regions even lacking a D” layer altogether.
  • The D” layer may also be where deep mantle plumes originate and where subducting slabs terminate.
  • The new research highlights the presence of a substantial amount of water within this global magma ocean. The exact origin of this water remains a topic of debate.
  • Some suggest that water would have concentrated towards the bottom of the magma ocean as it cooled, forming hydrous oceans. This hydrous magma ocean favoured the formation of an iron-rich phase called iron-magnesium peroxide.
  • 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, minerals in D” would be dominated by a new assemblage: the iron-poor silicate, iron-rich (Fe, Mg) peroxide, and iron-poor (Fe, Mg) oxide.
  • This iron-dominant peroxide also possesses low seismic velocities and high electrical conductivity, making it a potential candidate to explain the D” layer’s unique geophysical features.
  • The D” layer consists of ultra-low velocity zones (ULVZ) and layers of high conductance, both of which contribute to its well-known compositional heterogeneity.
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