<P> Based on the relative prevalence of various chemical elements in the Solar System, the theory of planetary formation, and constraints imposed or implied by the chemistry of the rest of the Earth's volume, the inner core is believed to consist primarily of a nickel - iron alloy . Pure iron was found to be denser than the core by approximately 3%, implying the presence of light elements in the core (e.g. silicon, oxygen, sulfur) in addition to the probable presence of nickel . </P> <P> Further, if the primordial and mostly fluid (still forming) earth contained any significant mass (es) of elements denser than iron and nickel, namely the white (appearance) precious metals (and a few others) except silver, specifically the siderophile elements, then these would necessarily have differentiated to the very center of the core into concentric nested spheres by planetary differentiation, with the most dense (and stable, i.e. platinum, iridium, and osmium, (etc .) in order of density) of these forming the innermost spheroid (s). While unstable elements of such trans - iron / nickel density would have mostly decayed to iron / nickel / lead by the time the earth formed a discrete core . </P> <P> It then necessarily follows that all, or almost all, of these denser elements we have mined (or are even able to) at the surface (or near surface, or even at all "above" the core) have been delivered later as part of impact objects / masses . </P> <P> The temperature of the inner core can be estimated by considering both the theoretical and the experimentally demonstrated constraints on the melting temperature of impure iron at the pressure which iron is under at the boundary of the inner core (about 330 GPa). These considerations suggest that its temperature is about 5,700 K (5,400 ° C; 9,800 ° F). The pressure in the Earth's inner core is slightly higher than it is at the boundary between the outer and inner cores: it ranges from about 330 to 360 gigapascals (3,300,000 to 3,600,000 atm). Iron can be solid at such high temperatures only because its melting temperature increases dramatically at pressures of that magnitude (see the Clausius--Clapeyron relation). </P>

Which of the following best describes the composition of the earth’s core