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 crystallized 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:
- solid-state convection inducing a preferred orientation of crystallites or
- 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)