Editing Core–mantle boundary (section)

== D″ region ==
An approximately 200&nbsp;km thick layer of the lower mantle directly above the CMB is referred to as the ''D″ region'' ("D double-prime" or "D prime prime") and is sometimes included in discussions regarding the core–mantle boundary zone.<ref name="Peltier">{{cite book <!--|chapter=Mantle dynamics and the D-doubleprime layer implications of the post-perovskite phase -->|contribution=Mantle Dynamics and the D" Layer: Impacts of the Post Perovskite Phase |author=WR Peltier |url=http://www.atmosp.physics.utoronto.ca/~peltier/pubs_books/W.R.%20Peltier,%20Mantle%20Dynamics%20and%20the%20D%20doubleprime%20Layer.Implications%20of%20the%20Post-perovskite%20Phase,%20AGU%20Geodynamics%20Series%20Monograph,%20AGU%20Books,%20pages%20217-227,%202007.pdf |year=2007  |pages=217–227 |title=Post-Perovskite: The Last Mantle Phase Transition|work=Volume 174 in AGU Geophysical Monographs|editor1=Kei Hirose |editor2=John Brodholt |editor3=Thome Lay |editor4=David Yuen |isbn=978-0-87590-439-9 |publisher=[[American Geophysical Union]]}}</ref> The D″ name originates from geophysicist [[Keith Edward Bullen|Keith Bullen]]'s designations for the Earth's layers. His system was to label each layer alphabetically, A through G, with the [[Earth's crust|crust]] as 'A' and the inner [[Internal structure of Earth#Core|core]] as 'G'. In his 1942 publication of his model, the entire lower mantle was the D&nbsp;layer. In 1949, Bullen found his 'D'&nbsp;layer to actually be two different layers. The upper part of the D layer, about 1,800&nbsp;km thick, was renamed D′ (D prime) and the lower part (the bottom 200&nbsp;km) was named D″.<ref>Bullen K., Compressibility-pressure hypothesis and the Earth’s interior. Monthly Notices of the Royal Astronomical Society, Geophysical Supplements, 5, 355–368., 1949 </ref>  Later it was found that D" is non-spherical.<ref> Creager, K.C. and Jordan, T.H. (1986). Asperical structure of the core-mantle boundary. Geophys. Res. Lett. 13, 1497-1500</ref> In 1993, Czechowski found that inhomogeneities in D" form structures analogous to continents (i.e. core-continents). They move in time and determine some properties of [[Hotspot (geology)|hotspot]]s and [[mantle convection]].<ref>Czechowski L. (1993) Geodesy and Physics of the Earth pp 392-395, The Origin of Hotspots and The D” Layer</ref> Later research supported this hypothesis.<ref>Torsvik, Trond H.; Smethurst, Mark A.; Burke, Kevin; Steinberger, Bernhard (2006). "Large igneous provinces generated from the margins of the large low-velocity provinces in the deep mantle". Geophysical Journal International. 167 (3): 1447–1460. Bibcode:2006GeoJI.167.1447T. doi:10.1111/j.1365-</ref>
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(Commenting this out until someone can make it make sense.) Slow small-scaled structures have been discovered on the core-mantle boundary; these are dubbed [[Ultra low velocity zone|ultra-low velocity zone]]s (ULVZs). It is suggested that large scale inhomogeneities of D" are formed by high density matter flowing on the core. Correlation between these inhomogeneities (c(ore)-continents)  and position of [[Hotspot (geology)|hotspots]] was found by 
<ref name="Czechowski">{{cite |title= The Origin of Hotspots and The D” Layer.|author1=Czechowski L.|journal=In: Montag H., Reigber C. (eds) Geodesy and Physics of the Earth. International Association of Geodesy Symposia|volume=112|pages=392–395}}</ref>
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