Editing Core–mantle boundary (section)

== Seismic discontinuity ==
A seismic discontinuity occurs within Earth's interior at a depth of about 2,900 km (1,800 mi) below the surface, where there is an abrupt change in the speed of seismic waves (generated by earthquakes or explosions) that travel through Earth.<ref>{{Cite journal|date=1981-06-01|title=Preliminary reference Earth model|journal=[[Physics of the Earth and Planetary Interiors]]|language=en|volume=25|issue=4|pages=297–356|doi=10.1016/0031-9201(81)90046-7|issn=0031-9201|bibcode=1981PEPI...25..297D|last1=Dziewonski|first1=Adam M.|last2=Anderson|first2=Don L.}}</ref> At this depth, primary seismic waves (P waves) decrease in velocity while secondary seismic waves (S waves) disappear completely. S waves shear material and cannot transmit through liquids, so it is thought that the unit above the discontinuity is solid, while the unit below is in a liquid or molten form.

The discontinuity was discovered by [[Beno Gutenberg]], a seismologist who made several important contributions to the study and understanding of the Earth's interior. The CMB has also been referred to as the [[Gutenberg discontinuity]], the Oldham-Gutenberg discontinuity, or the Wiechert-Gutenberg discontinuity.{{Citation needed|date=August 2018}}  In modern times, however, the term [[Lithosphere–asthenosphere boundary|Gutenberg discontinuity or the "G"]] is most commonly used in reference to a decrease in seismic velocity with depth that is sometimes observed at about 100 km below the Earth's oceans.<ref>{{Cite journal|last=Schmerr|first=N.|date=2012-03-22|title=The Gutenberg Discontinuity: Melt at the Lithosphere-Asthenosphere Boundary|journal=Science|volume=335|issue=6075|pages=1480–1483|doi=10.1126/science.1215433|pmid=22442480|issn=0036-8075|bibcode=2012Sci...335.1480S|s2cid=206538202}}</ref>