Seismologists see Earth's interior as interplay between temperature, pressure and chemistry

Surface topography and bathymetry around South America (top) overlays variable topography on Earth's upper mantle phase transition discontinuities at 410 km (middle) and 660 km (bottom) depth (topography is contoured in 2 km increments). Topography on the discontinuities is used to characterize compositional and thermal heterogeneity within the Earth. In this region, the large depressions are related to subduction processes, whereby cold oceanic lithosphere descends into the mantle. Credit: Nicholas Schmerr, Edward Garnero, Arizona State University