Editing Planetary core (section)

==Chemistry==

===Determining primary composition – Earth===

Using the chondritic reference model and combining known compositions of the [[Crust (geology)|crust]] and [[Mantle (geology)|mantle]], the unknown component, the composition of the inner and outer core, can be determined: 85% Fe, 5% Ni, 0.9% Cr, 0.25% Co, and all other [[refractory metal]]s at very low concentration.<ref name="Wood, Walter and Jonathan 2006" /> This leaves Earth's core with a 5–10% weight deficit for the outer core,<ref name="McDonough 2003">{{cite journal |last=McDonough |first=W. F. |title=Compositional Model for the Earth's Core |journal=Geochemistry of the Mantle and Core |location=Maryland |date=2003 |publisher=University of Maryland Geology Department |pages=547–568 }}</ref> and a 4–5% weight deficit for the inner core;<ref name="McDonough 2003" /> which is attributed to lighter elements that should be cosmically abundant and are iron-soluble; H, O, C, S, P, and Si.<ref name="Wood, Walter and Jonathan 2006"/> Earth's core contains half the Earth's [[vanadium]] and [[chromium]], and may contain considerable [[niobium]] and [[tantalum]].<ref name="McDonough 2003" /> Earth's core is depleted in [[germanium]] and [[gallium]].<ref name="McDonough 2003" />

===Weight deficit components – Earth===

[[Sulfur]] is strongly siderophilic and only moderately volatile and depleted in the silicate earth; thus may account for 1.9 weight&nbsp;% of Earth's core.<ref name="Wood, Walter and Jonathan 2006" />  By similar arguments, [[phosphorus]] may be present up to 0.2 weight&nbsp;%. Hydrogen and carbon, however, are highly volatile and thus would have been lost during early accretion and therefore can only account for 0.1 to 0.2 weight&nbsp;% respectively.<ref name="Wood, Walter and Jonathan 2006" /> [[Silicon]] and [[oxygen]] thus make up the remaining mass deficit of Earth's core; though the abundances of each are still a matter of controversy revolving largely around the pressure and oxidation state of Earth's core during its formation.<ref name="Wood, Walter and Jonathan 2006" /> No geochemical evidence exists to include any radioactive elements in Earth's core.<ref name="McDonough 2003" />  Despite this, experimental evidence has found [[potassium]] to be strongly siderophilic at the temperatures associated with core formation, thus there is potential for potassium in planetary cores of planets, and therefore [[potassium-40]] as well.<ref name="Murthy, van Westrenen and Fei 2003">{{cite journal |last1=Murthy |first1=V. Rama |last2=van Westrenen |first2=Wim |last3=Fei |first3=Yingwei |title=Experimental evidence that potassium is a substantial radioactive heat source in planetary cores |journal=Letters to Nature |volume=423 |issue=6936 |date=2003 |pages=163–167 |doi=10.1038/nature01560|pmid=12736683 |bibcode = 2003Natur.423..163M |s2cid=4430068 }}</ref>

===Isotopic composition – Earth===

[[Hafnium]]/[[tungsten]] (Hf/W) isotopic ratios, when compared with a chondritic reference frame, show a marked enrichment in the silicate earth indicating depletion in Earth's core. Iron meteorites, believed to be resultant from very early core fractionation processes, are also depleted.<ref name="Wood, Walter and Jonathan 2006" /> [[Niobium]]/[[tantalum]] (Nb/Ta) isotopic ratios, when compared with a chondritic reference frame, show mild depletion in bulk silicate Earth and the moon.<ref name="Hauck and Van Orman 2011">{{cite journal |last1=Hauck |first1=S. A. |last2=Van Orman |first2=J. A. |title=Core petrology: Implications for the dynamics and evolution of planetary interiors |journal= AGU Fall Meeting Abstracts|volume=2011 |publisher=American Geophysical Union |date=2011 |pages=DI41B–03 |bibcode=2011AGUFMDI41B..03H }}</ref>

===Pallasite meteorites===
[[Pallasite]]s are thought to form at the [[core-mantle boundary]] of an early planetesimal, although a recent hypothesis suggests that they are impact-generated mixtures of core and mantle materials.<ref>Edward R. D. Scott, "Impact Origins for Pallasites," Lunar and Planetary Science XXXVIII, 2007.</ref>