Helium Feels the Heat in Earth's Mantle

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Science  16 Dec 2005:
Vol. 310, Issue 5755, pp. 1777-1778
DOI: 10.1126/science.1120194

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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.