The D'' (Dee double prime) layer surrounds the Earth's core and is between 0 and 300 km thick (variable thickness). It is at the interface between two chemically distinct regions, the rocky mantle and the metallic core.This may be the most dynamic and active zone in the Earth’s interior. It has some strange seismic properties and for some time scientists have discussed its probable main composition.
In 2004 Japanese researchers found that high temperatures and pressures like those existing in the D” layer transform perovskite, the major mineral in Earth's mantle, into a new mineral called post-perovskite. New research published on 17 January 2006 in Proceedings of the National Academy of Science of USA seem to confirm that the seismic properties of post-perovskite are much like the previously inexplicable properties found in the D'' layer. This is convincing evidence that post-perovskite is in the D'' layer and produces its strange seismic properties.
