Carbon core compositional model

The compositional model for the core has a light element composition that seeks to ht the density requirements for the outer core and is consistent with cosmochemical constraints. Signihcantly, along with iron and nickel the core contains most of the planet s sulfur, phosphorus, and carbon budget. Finally, this model composition is notable in that it is devoid of radioactive elements. The discussion that follows reviews the issues associated with compositional models for the core. 

Silicates provide further evidence for the unusual origin of lAB-IIICD. While differentiated silicates might be expected in association with iron meteorites, silicates in lAB-IIICD irons are broadly chondritic (Mittlefehldt et al., 1998 Benedix et al., 2000 see Chapter 1.11). Models for the origins of lAB-IIICD iron meteorites include crystallization of a sulfur- and carbon-rich core in a partially differentiated object (Kracher, 1985 McCoy et al., 1993), breakup and reassembly of a partially differentiated object at its peak temperature (Benedix et al., 2000), or crystal segregation in isolated impact melt pools on the surface of a porous chondritic body (Wasson and Kallemeyn, 2002). A recent compilation of the chemical compositions of lAB and IIICD iron meteorites may be found in Wasson and KaUemeyn (2002). 

Figure 6 The Holocene ice-core record of the variability of methane, carbon dioxide, and S C02- (a) The methane record from ice cores in Greenland and Antarctica, showing significant variability including variability in the interpolar gradient (Chappellaz et al., 1997). (b) The results of a three-box model used to infer the latitudinal distribution sources of methane at four different time spans during the Holocene Epoch (Chappellaz et al., 1997). (c, d) The carbon dioxide concentration and its isotopic composition from Taylor Dome, Antarctica (Indermuhle et al., 1999). Note the dissimilarities among the trends in this figure (Raynaud et al. (2000) reproduced by permission of Elsevier from Quat. Set. Rev., 2000, 19, 9-17 (figure 1)).

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