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
  or
  2. crystal growth with a preferred orientation



Temperature: 

- 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)