The mantle comprises that part of the Earth between the Mohorovičić and the Wiechert–Gutenberg discontinuities. It makes up 83 percent of the volume of the Earth and 67 percent of its mass and is thus of decisive importance in determining the bulk composition of the planet. In estimating elemental abundances in the mantle, however, the same difficulty as with the core arises: direct sampling is not feasible. Much more geophysical data are available for the mantle, however, and some volcanic eruptions have brought rock fragments to the surface that have certainly been derived from this zone. The most remarkable of ...(100 of 18829 words)