Geophysics

Gradation of Fabric

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Science  12 Aug 2005:
Vol. 309, Issue 5737, pp. 991
DOI: 10.1126/science.309.5737.991a

The solid inner core of Earth grew larger over time as the liquid iron outer core crystallized. This process released latent heat that helps drives convection in the liquid outer core, producing Earth's magnetic field; the inner core now has a radius of about 1200 km. Recent seismic observations have started to reveal details of the inner parts of the inner core. Initial results showed that the core has a distinct and organized crystal fabric. More recently, it has been suggested that there may be a boundary deep in the inner core at a radius of about 300 km, which may indicate its episodic growth. Cormier and Stroujkova searched for additional evidence of such a structure in a series of waveforms of seismic waves passing through the inner core at various angles (thus sampling it through different depths). The data suggest, albeit not conclusively, more subtle variations in the fabric of the inner core with depth, consistent with an increase in organized crystal size with depth, instead of a sharp transition. — BH

Earth Planet. Sci. Lett. 236, 96 (2005).

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