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).
