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The Back Cover:
Viscosity Field in Earth's Mantle


A visualization of the viscosity field in a model of the Earth's mantle and lithosphere by Paul Tackley of UCLA. Tackley is investigating how mantle behavior gives rise to our planet's three different types of plate boundaries: mid-ocean ridges, subduction zones, and transform faults. The image indicates viscosity (red is high) and velocity vectors. Tackley's models are the first to show self-consistent plate generation as the natural outcome of a mantle convection simulation; previous models did not give rise to separate lithospheric plates.