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Science 24 June 2005:
Vol. 308. no. 5730, pp. 1892 - 1894
DOI: 10.1126/science.1111724
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Reports

Sound Velocities of Hot Dense Iron: Birch's Law Revisited

Jung-Fu Lin,1* Wolfgang Sturhahn,2 Jiyong Zhao,2 Guoyin Shen,3 Ho-kwang Mao,1 Russell J. Hemley1

Sound velocities of hexagonal close-packed iron (hcp-Fe) were measured at pressures up to 73 gigapascals and at temperatures up to 1700 kelvin with nuclear inelastic x-ray scattering in a laser-heated diamond anvil cell. The compressional-wave velocities (VP) and shear-wave velocities (VS) of hcp-Fe decreased significantly with increasing temperature under moderately high pressures. VP and VS under high pressures and temperatures thus cannot be fitted to a linear relation, Birch's law, which has been used to extrapolate measured sound velocities to densities of iron in Earth's interior. This result means that there are more light elements in Earth's core than have been inferred from linear extrapolation at room temperature.

1 Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, N.W., Washington, DC 20015, USA.
2 Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439, USA.
3 Consortium for Advanced Radiation Sources, The University of Chicago, Chicago, IL 60637, USA.

* To whom correspondence should be addressed. E-mail: j.lin{at}gl.ciw.edu

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