The lower reaches of the Earth’s mantle extend all the way down to the boundary with the metallic core, which lies about 2,900 kilometers below the surface.  We knew almost nothing about this highly inaccessible region until good seismic measurements became available in the 1970s.  That coincided with a rapid increase in computer power, which enabled seismologists to generate images, albeit at very low resolution, of the entire mantle.  The images surprised us by revealing some dramatic features in the lower mantle.
Allen McNamara is a Professor of Geological Sciences at Michigan State University.  He uses computer-based fluid mechanical models to investigate the behavior of the mantle, working in tandem with the seismologists to understand the origin and dynamics of these recently discovered features in the mantle.