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Science 16 December 2005:
Vol. 310. no. 5755, pp. 1777 - 1778
DOI: 10.1126/science.1120194
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Perspectives

GEOPHYSICS:
Helium Feels the Heat in Earth's Mantle

Francis Albarède

In the 1990s, the model of Earth's mantle as two separately convecting layers was challenged by seismic measurements. Despite this, several arguments survive that support separate mantle layers divided by a discontinuity at 660-kilometer depth. One cornerstone of the two-layer model is a pronounced imbalance between fluxes of heat and helium from the crust. The small helium flux suggests the existence of a boundary layer blocking the helium flow, which might be interpreted as the 660-kilometer discontinuity. In his Perspective, Albarède discusses a recent paper in Earth and Planetary Science Letters by Castro et al. in which a computer simulation supports a new view of the heat-helium flux problem. Instead of the 660-kilometer discontinuity slowing the helium flow, aquifer layers in Earth's crust could be responsible for the imbalance.

The author is in the Laboratoire des Sciences de la Terre, Ecole Normale Supérieure de Lyon, 46 Allee d'Italie, 69364 Lyon Cedex 7, France. E-mail: francis.albarede{at}ens-lyon.fr

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Science. ISSN 0036-8075 (print), 1095-9203 (online)