On the Coupling of the Earth’s Core and Mantle During the 26,000-Year Precession

  • Alar Toomre


Recent papers by Malkus (1963) and by Stewartson and Roberts (1963) have raised anew the question of the identity of the coupling mechanism whereby the liquid core of the Earth is induced to partake in the luni-solar (or 26,000-year) precession of the mantle. That the angular momentum vector of the core indeed must precess with the same period and approximately with the same angular amplitude as the exterior can hardly be doubted. Bullard (1949), in particular, has pointed out that if that were not the case, the resulting magnetic effects would almost certainly be too violent to have gone unnoticed. It is readily estimated, however, that the direct lunar and solar gravitational torques on the core total only about three-quarters of the value needed to make it precess at such a rate, on account of the core being denser and therefore more nearly spherical than this planet as a whole. Hence the problem of accounting for the manner in which the remaining one-quarter or so of the required moment manages to be conveyed from the mantle to the fluid within.


Lower Mantle Interaction Torque Angular Momentum Vector Core Fluid Gravitational Torque 
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© Plenum Press 1966

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  • Alar Toomre

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