Materials science issues in the Earth and planetary sciences

Abstract

Earth is a dynamic planet. Solid state convection in the deep interior is coupled to the motion of about a dozen rigid plates at the surface. Earthquakes, volcanoes and mountains are located mainly at the boundaries between plates and reflect the relative motion between them. The associated deformation processes span a wide range of regimes from high temperature dislocation and diffusion accommodated creep to brittle fracture, friction, fragmentation and granular flow. There is a long history of collaboration between earth and materials scientists in modeling the relevant micromechanics and formulating appropriate constitutive relations. Materials analysis in the Earth and planetary sciences pose special challenges. Pressure and temperature conditions in the Earth's interior reach 360 GPa and 8000 K so that constitutive equations must often be extended to pressure and temperature regimes well beyond laboratory limits. Deformation occurs over a range of temporal and spatial scales difficult to simulate in the laboratory. The emergence of deformation structures spanning many spatial orders of magnitude has made Earth sciences the test bed for modern ideas of self-organization and scaling. Finally, deformation mechanisms in earth materials are extremely sensitive to environmental factors, especially water. This factor alone explains most differences between large-scale deformation structures observed on Earth and those on the other terrestrial planets. Current problems in the Earth sciences that require a better understanding of material behavior include the mechanics of the earthquake instability, the migration of magma in the crust, the source and dynamical significance of observed heterogeneity in the deep interior, and the generation of the magnetic field.