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Evidencia en contra de una Tierra condrítica.
Ian H Campbell1, Hugh St C O'Neill
1Research School of Earth Science, Australian National University, Canberra, Australian Capital Territory 0200, Australia. Ian.Campbell@anu.edu.au
Nature
|March 31, 2012
Resumen
La proporción de isótopos de neodimio de la Tierra excede el valor solar, lo que desafía el modelo de la Tierra condrítica. Esto sugiere ya sea material de formación no-condrítico o pérdida de materia a través de la erosión por colisión.
Área de la Ciencia:
- La geoquímica es la geoquímica.
- Ciencias planetarias Ciencias planetarias.
- La geoquímica de los isótopos es la geoquímica de los isótopos.
Sus antecedentes:
- El modelo de la "Tierra condrítica" asume que el componente de silicato de la Tierra refleja los meteoritos condríticos.
- La proporción terrestre (142) Nd / (144) Nd es mayor que la proporción solar (condrítica), lo que crea una paradoja geoquímica.
- Una capa profunda del manto enriquecida con elementos incompatibles, una solución propuesta, entra en conflicto con el flujo de calor de la pluma del manto.
Objetivo del estudio:
- Para investigar la discrepancia entre la relación de isótopos de neodimio de la Tierra y el valor solar/condrítico.
- Evaluar los modelos existentes para la formación y composición de la Tierra.
- Proponer explicaciones alternativas para las paradojas geoquímicas.
Principales métodos:
- Análisis de las proporciones de isótopos de neodimio ((142) Nd / ((144) Nd) en los materiales de la Tierra.
- Comparación de las composiciones isotópicas de los meteoritos terrestres y condríticos.
- Modelado termodinámico y geológico de la formación y evolución planetaria.
Principales resultados:
- La relación (142) Nd / (144) Nd de la Tierra es demostrablemente mayor que la relación solar inferida.
- La hipótesis de la "capa oculta" es inconsistente con las características observadas de la pluma del manto.
- Los datos apoyan ya sea una composición inicial no condrítica para la Tierra o una pérdida significativa de materia durante la formación.
Conclusiones:
- La suposición fundamental de una "Tierra condrítica" puede ser incorrecta.
- Se favorecen escenarios de formación alternativos, incluida la acreción no condrítica o la erosión por colisión.
- Es necesario revisar nuestra comprensión de la composición masiva de la Tierra y su historia temprana.
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