Publication: Adiós a la astenosfera
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2002
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Asociación Española para la Enseñanza de las Ciencias de la Tierra
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Abstract
La idea de un nivel profundo que se deformase plásticamente ("astenosfera") surgió de la mano de la isostasia, pero se convirtió en un imperativo con la revolución movilista. Creyendo que el manto inferior era demasiado rígido para fluir, los geofísicos de los años 60 se apresuraron, con una conducta que se nos antoja muy poco científica, a proclamar, basándose en la existencia de zonas dispersas del manto superior con velocidades sísmicas bajas, que habían identificado el "necesario" nivel de despegue de la litosfera respecto al resto del manto. La dependencia artificial del paradigma movilista con respecto a esta capa llevó a muchos científicos a inauditas defensas de una astenosfera global contra los datos que ellos mismos presentaban. La tomografía sísmica, que ha revelado que todo el manto terrestre fluye, ha permitido una vuelta, aún incompleta, a la realidad, en la que la astenosfera comienza a ser descartada tanto por innecesaria como por inexistente. Sin embargo, apenas se han producido rectificaciones explícitas, y tanto muchos textos como artículos científicos siguen empleando el viejo término. El surgimiento, evolución y defunción de este concepto puede servir como un excelente ejemplo de aula sobre el funcionamiento de la Ciencia real.
The notion of a deep plastic layer ("asthenosphere") in the Earth was born soon after isostasy was accepted as an important tenet in Earth Sciences. With the mobilist revolution, asthenosphere became a "must" and, judging the lower mantle too rigid to flow, geophysicists of the 60's hurried, acting in what now seems a very unscientific manner, to claim they had located the necessary layer in low seismic velocity areas of the upper mantle. The created dependence on the asthenosphere concept of the plate tectonics paradigm brought about incredible situations, in which scientific teams defended the idea of a global plastic layer in the upper mantle against the face value of their own data. Seismic tomography, which has shown a flow through the whole mantle, has marked a return, still incomplete, to reality, where the asthenosphere concept is being discarded as unnecessary and (especially) non-existent. Nevertheless, explicit retractions of this concept have been scarce, whereby it is still present in many textbooks and scientific articles. We contend that the appearance, evolution and demise of this term can constitute an excellent classroom example of the workings of real Science.
The notion of a deep plastic layer ("asthenosphere") in the Earth was born soon after isostasy was accepted as an important tenet in Earth Sciences. With the mobilist revolution, asthenosphere became a "must" and, judging the lower mantle too rigid to flow, geophysicists of the 60's hurried, acting in what now seems a very unscientific manner, to claim they had located the necessary layer in low seismic velocity areas of the upper mantle. The created dependence on the asthenosphere concept of the plate tectonics paradigm brought about incredible situations, in which scientific teams defended the idea of a global plastic layer in the upper mantle against the face value of their own data. Seismic tomography, which has shown a flow through the whole mantle, has marked a return, still incomplete, to reality, where the asthenosphere concept is being discarded as unnecessary and (especially) non-existent. Nevertheless, explicit retractions of this concept have been scarce, whereby it is still present in many textbooks and scientific articles. We contend that the appearance, evolution and demise of this term can constitute an excellent classroom example of the workings of real Science.