Ref: http://focus.aps.org/story/v13/st1
http://focus.aps.org/stories/v13/st1/pic-v13-st1-1.gif
Phys. Rev. Lett. 92, 018501
Like bats using echolocation to navigate through the night,
geophysicists rely on seismic waves for information on the Earth's
deep interior. Almost everything known about that inaccessible region
is inferred from the speed of sound waves generated by earthquakes.
In the 9 January PRL, however, a team describes a calculation of the
properties of the Earth's lower mantle starting from basic physics
principles. The results disagree slightly with seismic data and
suggest that the structure of minerals in the Earth's lower mantle is
more complex than geophysicists have assumed.
The Earth has an iron core surrounded by a dense layer called the
mantle, which is capped with a thin rind of rocky crust. Seismic
measurements reveal the density and elasticity of the mantle, but not
much about its composition. Perovskite, the mineral that dominates
the lower mantle, contains mainly magnesium, silicon, and oxygen, but
researchers suspect that a lot of iron and aluminum are present as
impurities. Exactly how much isn't known, nor how these impurities
would affect the elasticity of the rock. To further complicate the
mystery, minerals often behave in unexpected ways at the extreme
pressures found 1000 kilometers underground. Iron, for example,
becomes non-magnetic and may tend to migrate from perovskite toward
another mineral called magnesiumwustite, as the pressure rises.
See: http://focus.aps.org/story/v13/st1
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