‘Missing silicon problem’ solved, say geophysicists

Published in Physics World, 3 May 2012

Researchers in Japan have new evidence that the Earth’s lower mantle contains more silicon than its upper mantle. The results suggest that the composition of the Earth’s silicates match the type of meteorites thought to exist in the solar nebula from which the Earth was created.

The Earth’s mantle can be divided into three sections: the upper mantle, which stretches from the thin crust down to about 400 km in depth; a transition zone of about 250 km; and finally the lower mantle, which stretches from the transition zone to about 2900 km in depth. Most geoscientists agree that the upper mantle is composed mostly of peridotite, a dense igneous rock containing a high proportion of the mineral olivine (Mg,Fe)2SiO4. At the transition zone, a change in the way seismic waves propagate has generally been explained by a phase transition in the structure of the olivine, suggesting that the lower mantle, too, is peridotite in composition. If this is true, however, the Earth would contain far less silicon than chondritic meteorites – the type of meteorites thought to exist at the time of the Earth’s formation. […]

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