Core composition

Outer Core solid metallic alloy

-> mainly Fe and Ni + eighter elements such as S and O
-> less probable or less significant: Si, Ni, H, Mg

Arguments for light element determination mainly follows from considerations on:

-> abundance in the Earth's mantle, relative to cosmic abundances,
but losses due to volatility have to be considered too
(e.g. H very abundant in universe but high losses due to volatility)
-> ability to form alloys as seen in laboratory experiments and meteorites
-> ability to lower the density of the core (e.g. good for S, bad for Ni)
For details, see Jeanloz, 1990, Annu. Rev. Earth Planet. Sci., 18, 357-386.

Inner Core solid cristallyed Fe-Ni alloy

-> may be partially molten
-> likely to be convectively unstable on very long time scales (see mantle)
-> seismic travel time anomalies interpreted as a preferred orientation of the
cristals rather than lateral heterogeneities
this seismic anisotropy is caused by:
1. solid-state convection inducing a preferred orientation of crystallites
2. crystal growth with a preferred orientation


- at CMB: 4000 ± 500 K
- centre: 5000-6000 K

CMB, core side: mush zone

O, Si, Mg intermixed within iron-alloy fluid core-mantle reaction in mush zone => composition of core increasingly contaminated by mantle (O most important)