The mesosphere refers to the lower mantle in the region between the asthenosphere and the outer core. It is the largest layer of the earth. The upper boundary is poorly constrained, but occurs where the more ductile asthenosphere transitions to more rigid material. As depth increases, pressure builds and forces atoms into a denser, more rigid structure; thus the difference between mesosphere and asthenosphere is likely due only to a density difference, and not to any difference in composition. This transition is thought to occur at roughly 700 kilometers depth. This measurement is estimated from seismic data.
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| Crust • Upper mantle • Lithosphere • Asthenosphere • Mesosphere • Mantle • Outer core • Inner core • Plate tectonics |
