Editing Geochemistry (section)

===Solar System===
[[File:ElementalAbundance.svg|thumb|upright=1.7|Abundances of Solar System elements.<ref>Data from table 6 of {{cite journal|last1=Cameron|first1=A.G.W.|title=Abundances of the elements in the solar system|journal=Space Science Reviews|date=September 1973|volume=15|issue=1|pages=121|doi=10.1007/BF00172440|bibcode=1973SSRv...15..121C|s2cid=120201972}}</ref>]]
The composition of the [[Solar System]] is similar to that of many other stars, and aside from small anomalies it can be assumed to have formed from a [[solar nebula]] that had a uniform composition, and the composition of the [[Sun]]'s [[photosphere]] is similar to that of the rest of the Solar System. The composition of the photosphere is determined by fitting the [[Spectral line|absorption lines]] in its [[spectrum]] to models of the Sun's atmosphere.<ref name=Palme>{{cite book|first1=H.|last1=Palme|first2=A.|last2=Jones|chapter=1.03 &ndash; Solar system abundance of the elements|editor-last1=Holland|editor-first1=H.D.|editor-last2=Turekian|editor-first2=K.K.|title=Treatise on Geochemistry|volume=1: Meteorites, Comets and Planets|date=2003|publisher=Elsevier Science|location=Oxford|isbn=9780080437514|doi=10.1016/B0-08-043751-6/01060-4|pages=41&ndash;61|edition=1st|chapter-url=https://www.elsevier.ca/brochures/treatiseongeochemistry/contents/sample1.pdf|access-date=3 October 2017|archive-date=3 October 2017|archive-url=https://web.archive.org/web/20171003225547/https://www.elsevier.ca/brochures/treatiseongeochemistry/contents/sample1.pdf|url-status=dead}}</ref> By far the largest two elements by fraction of total mass are hydrogen (74.9%) and [[helium]] (23.8%), with all the remaining elements contributing just 1.3%.<ref>{{cite journal|last1=Lodders|first1=Katharina|author1-link=Katharina Lodders|title=Solar System Abundances and Condensation Temperatures of the Elements|journal=The Astrophysical Journal|date=10 July 2003|volume=591|issue=2|pages=1220–1247|doi=10.1086/375492|bibcode=2003ApJ...591.1220L|citeseerx=10.1.1.695.5451|s2cid=42498829 }}</ref> There is a general trend of [[Exponential decay|exponential decrease]] in abundance with increasing atomic number, although elements with even atomic number are more common than their odd-numbered neighbors (the [[Oddo–Harkins rule]]). Compared to the overall trend, [[lithium]], [[boron]] and [[beryllium]] are depleted and iron is anomalously enriched.<ref>{{cite book|last1=Middlemost|first1=Eric A. K.|title=Magmas, Rocks and Planetary Development: A Survey of Magma/Igneous Rock Systems|date=2014|publisher=Routledge|isbn=9781317892649}}</ref>{{rp|284&ndash;285}}

The pattern of elemental abundance is mainly due to two factors. The hydrogen, helium, and some of the lithium were [[Big Bang nucleosynthesis|formed in about 20 minutes after the Big Bang]], while the rest were [[Stellar nucleosynthesis|created in the interiors of stars]].<ref name=McSween/>{{rp|316&ndash;317}}