D″ is the rather obscure name for the lowermost mantle adjacent to the liquid core. The encyclopedia contains several articles on the properties of D″ because of its potential influence on the geodynamo. F is the name for the boundary layer at the bottom of the outer core, where liquid core material freezes and differentiates. K.E. Bullen, in 1940–1942, defined the layers of the Earth on the basis of extensive seismological studies linked to probable compositional and mineralogical models. He labelled the layers A to G from the top down, with A the crust, B the upper mantle, C the transition zone, D the lower mantle, E the liquid core, F the layer around the inner core, and G the solid inner core itself (see Earth structure, major divisions ).
The F‐layer was originally proposed to explain a transition region at the bottom of the outer core, introduced by H. Jeffreys in 1939, in which the P‐wave velocity decreased with depth. A similar structure was proposed by Gutenberg (1959)....
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Bibliography
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Gubbins, D. (2007). D″ and F‐layers. In: Gubbins, D., Herrero-Bervera, E. (eds) Encyclopedia of Geomagnetism and Paleomagnetism. Springer, Dordrecht. https://doi.org/10.1007/978-1-4020-4423-6_59
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