The Earth's Core

Earth's core formed very early in the planet's history, and is thought to have carried with it atomic species other than iron. Although it is isolated from the surface, it influences our environment through the production of Earth's magnetic field. To understand the process by which the field is generated and how it changes with time, several properties of iron and iron alloys must be understood first. Along with major advances in experimental methods, first principles studies of iron have contributed substantially to our understanding of Earth's core over the last several years. Future progress demands a consideration of iron with other alloying elements. We know light elements must be present in the solid inner core and liquid outer core from seismic density measurements. The major candidates are O, Si, and S, although, in principle their identity is virtually unconstrained. Important recent work has shown one possible way to calculate the concentration of individual light elements in the inner and outer parts. But major questions remain regarding: a) phase relations in the solid. Is the amount of light element in the inner core sufficient to stabilize new crystalline phases? b) What is the liquidus temperature of the outer core alloy (and therefore the temperature at the inner core boundary)? c) How does simultaneous consideration of multiple alloying elements change the partitioning determined with a single element? (Siepmann, Allen, Gillan, and Price).

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