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Science 27 January 1984:
Vol. 223. no. 4634, pp. 347 - 355
DOI: 10.1126/science.223.4634.347
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Articles

The Earth as a Planet: Paradigms and Paradoxes

Don L. Anderson 1

1 Professor of geophysics and director of the Seismological Laboratory, California Institute of Technology, Pasadena 91125.

The independent growth of the various branches of the earth sciences in the past two decades has led to a divergence of geophysical, geochemical, geological, and planetological models for the composition and evolution of a terrestrial planet. Evidence for differentiation and volcanism on small planets and a magma ocean on the moon contrasts with hypotheses for a mostly primitive, still undifferentiated, and homogeneous terrestrial mantle. In comparison with the moon, the earth has an extraordinarily thin crust. The geoid, which should reflect convection in the mantle, is apparently unrelated to the current distribution of continents and oceanic ridges. If the earth is deformable, the whole mantle should wander relative to the axis of rotation, but the implications of this are seldom discussed. The proposal of a mantle rich in olivine violates expectations based on evidence from extraterrestrial sources. These and other paradoxes force a reexamination of some long-held assumptions.


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