This page is currently under construction, just like our understanding of the core-mantle boundary. In the meantime, here's a sample model:
This figure shows results of a computer simulation of convection in the Earth's mantle. This plot grew out of the need to present a complex flow that varies in time and space on a 2-dimensional surface.
The computer simulation shows the results of chemical and thermal interaction between the Earth's mantle and molten iron outer core. A dense, iron-rich layer develops at this interface. In this figure, a "slice" of temperature in the lower mantle, but above the iron rich layer, is plotted over time. In this space-time-temperature graphic, the horizontal axis represents a physical location; the vertical axis represents time. Heat from the core creates hot "plumes" of upwelling material (red); cold downwellings (blue) simultaneously sink through the mantle. The red "streaks" represent the paths of plumes of hot material over time; forks in these streaks show plumes merging together. The horizontal axis represents about 10,000 km; the time axis shows approximately 700 million years.
We have published papers on this subject in Geophysical Research Letters and Journal of Geophysical Research (see publications list).
An iron-rich layer like the one that develops in these calculations has been proposed on the basis of seismological observations; these calculations illustrate how such a layer might grow in the Earth. The layer could have a significant effect on the development of plumes in the mantle and may also influence the evolution of the Earth's magnetic field.
Calculations and image by Nancy Montague and Louise Kellogg.
A recent Perspective in Science on the core-mantle boundary.
A past AGU abstract on this subject