Earth’s mysterious D” layer

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


•    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 
•    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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