THERMODYNAMICS FOR A SMALL PLANET (INVITED PAPER)

Cycles and feedback loops – sinking slabs and rising plumes, biogeochemical cycles, ocean-atmosphere interactions, the Gaia hypothesis, global warming, cradle-to-grave resource management – all these acknowledge the robustness and simultaneous fragility of Spaceship Earth. Thermodynamics is the driver, guardian, and policeman of all these processes; one has to know which way is downhill. During my 40+ years in science, the two most exciting new Earth materials have been silicate perovskite (and new postperovskite) and methane hydrate, each speaking to different geochemical regimes yet each important to the planet as a whole and to other planets. Among more familiar materials, a major realization is that size makes a difference, and nanoparticles often dominate reactivity. Anthropogenic materials, both technologically useful ones and their undesirable degradation products, need structural, thermodynamic and kinetic characterizations.

A mineralogist's crystal ball is far from perfect, but I highlight the following as areas where thermodynamics will be essential and exciting. The wealth of chemical and pressure and temperature environments suggested by the discovery of hundreds of extrasolar planets begs for systematic thermodynamic study by both computational and experimental means. The management of resources to produce energy (nuclear, solar, hydrogen, biofuel, etc.) requires full thermodynamic analysis. The control and remediation of past, present, and future pollution require thermodynamic and kinetic data. The incorporation of such data into risk assessment models is a major challenge and opportunity. Finally, and from a more fundamental point of view, integrating thermodynamic measurement, spectroscopic, diffraction, and imaging capabilities of increasing resolution, and sophisticated molecular-scale modeling will strengthen the link between microscopic and macroscopic that is the major goal of modern mineralogy and modern physics.