Editing Core–mantle boundary (section)

{{Short description|Discontinuity where the bottom of the planet's mantle meets the outer layer of the core}}
[[File:Slice earth.svg|thumb|Schematic view of the interior of Earth. {{olist |{{legend|#dd8714|[[continental crust]]}} |{{legend|#b8d2fe|[[oceanic crust]]}} |{{legend|#81ff7a|upper [[Earth's mantle|mantle]]}} |{{legend|#2dcf20|lower mantle}} |{{legend|#f4a828|[[Earth's outer core|outer core]]}} |{{legend|#f72b2e|[[Earth's inner core|inner core]]}}}}{{olist |list-style-type=upper-alpha |[[Mohorovicic discontinuity]] |'''core–mantle boundary''' |outer core–inner core boundary}}]]

The '''core–mantle boundary''' ('''CMB''') of Earth lies between the planet's [[silicate]] [[Earth's mantle|mantle]] and its liquid [[iron–nickel alloy|iron–nickel]] [[Earth's outer core|outer core]], at a depth of {{cvt|2,891|km|mi}} below Earth's surface. The boundary is observed via the discontinuity in [[seismic wave]] velocities at that depth due to the differences between the [[acoustic impedance]]s of the solid mantle and the molten outer core. [[P-wave]] velocities are much slower in the outer core than in the deep mantle while [[S-wave]]s do not exist at all in the liquid portion of the core. Recent evidence suggests a distinct boundary layer directly above the CMB possibly made of a novel phase of the basic [[silicate perovskite|perovskite]] mineralogy of the deep mantle named [[post-perovskite]]. [[Seismic tomography]] studies have shown significant irregularities within the boundary zone and appear to be dominated by the African and Pacific [[Large low-shear-velocity provinces]] (LLSVP).<ref name="LLSVP">{{cite journal|author1=Lekic, V.|author2=Cottaar, S.|author3=Dziewonski, A.|author4=Romanowicz, B.|name-list-style=amp|year=2012|title=Cluster analysis of global lower mantle|journal=[[Earth and Planetary Science Letters]]|volume=357-358|issue=1–3|pages=68–77|doi=10.1016/j.epsl.2012.09.014|bibcode=2012E&PSL.357...68L}}</ref>

The uppermost section of the outer core is thought to be about 500–1,800 K hotter than the overlying mantle, creating a thermal boundary layer.<ref>{{Cite journal|last1=Lay|first1=Thorne|last2=Hernlund|first2=John|last3=Buffett|first3=Bruce A.|date=2008|title=Core–mantle boundary heat flow|journal=[[Nature Geoscience]]|volume=1|issue=1|pages=25–32|doi=10.1038/ngeo.2007.44|issn=1752-0894|bibcode=2008NatGe...1...25L}}</ref> The boundary is thought to harbor topography, much like Earth's surface, that is supported by solid-state convection within the overlying mantle.{{Citation needed|date=August 2018}} Variations in the thermal properties of the CMB may affect how the outer core's iron-rich fluids flow, which are ultimately responsible for [[Earth's magnetic field]].{{Citation needed|date=August 2018}}