2006 Wood et al., Accretion of the Earth and segregation of its core (1119308), страница 6
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Thus, the Hf–W age of the Earth could reasonablyrefer to the earliest phases of core formation and the U–Pb age to thelast. To test this hypothesis properly it will be necessary to obtainexperimental data on the partitioning of Pb between silicates andmetals as a function of oxygen fugacity, pressure, temperature andsulphur content.The density of the liquid outer core is about 8% lower than pure Fealloy under core conditions, implying the presence of low-atomicnumber alloying elements.
Cosmochemical arguments suggest thatS, H and C are present at concentrations of 1.9, 0.1 and 0.2 wt%respectively. Si is a cosmochemically abundant element which dissolves readily in iron under reducing conditions and at high pressuresand temperatures. The accretion model discussed earlier, in whichincreases in oxygen fugacity accompany core segregation, leads(given a mantle Si content of 21 wt%; refs 3, 26) to 4–5% Si in thecore. The remaining potentially important component, oxygen, ismore difficult to constrain because the available experimental dataconflict with one another. Estimates based on some recently published data73 lead, under the conditions of core segregation impliedby siderophile element partitioning, to ,1 wt% oxygen in the core.Other recent data76 imply that the core should be richer in oxygenthan in silicon.
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