Editing Noble gas (section)

==== Argon ====
[[Isotopes of argon|Argon]] has three stable isotopes: <sup>36</sup>Ar, <sup>38</sup>Ar and <sup>40</sup>Ar. <sup>36</sup>Ar and <sup>38</sup>Ar are [[Primordial nuclide|primordial]], with their inventory on the earth's crust dependent on the equilibration of [[meteoric water]] with the crustal fluids.<ref name="Ballentine-2002b"/> This explains huge inventory of <sup>36</sup>Ar in the atmosphere. Production of these two isotopes (<sup>36</sup>Ar and <sup>38</sup>Ar) is negligible within the earth's crust, only limited concentrations of <sup>38</sup>Ar can be produced by interaction between alpha particles from decay of <sup>235,238</sup>U and <sup>232</sup>Th and light elements (<sup>37</sup>Cl and <sup>41</sup>K). While <sup>36</sup>Ar is continuously being produced by Beta-decay of <sup>36</sup>Cl.<ref name="Wetherill 679–683"/><ref>{{Cite journal |last1=Fleming |first1=W. H. |last2=Thode |first2=H. G. |date=1953-10-15 |title=Neutron and Spontaneous Fission in Uranium Ores |url=https://link.aps.org/doi/10.1103/PhysRev.92.378 |journal=Physical Review |language=en |volume=92 |issue=2 |pages=378–382 |doi=10.1103/PhysRev.92.378 |bibcode=1953PhRv...92..378F |issn=0031-899X}}</ref> <sup>40</sup>Ar is a product of radiogenic decay of <sup>40</sup>K. Different endmembers values for <sup>40</sup>Ar/<sup>36</sup>Ar have been reported; Air = 295.5,<ref name="Burnard-1997">{{Cite journal |last1=Burnard |first1=Pete |last2=Graham |first2=David |last3=Turner |first3=Grenville |date=1997-04-25 |title=Vesicle-Specific Noble Gas Analyses of "Popping Rock": Implications for Primordial Noble Gases in Earth |url=http://dx.doi.org/10.1126/science.276.5312.568 |journal=Science |volume=276 |issue=5312 |pages=568–571 |doi=10.1126/science.276.5312.568 |pmid=9110971 |issn=0036-8075}}</ref> MORB = 40,000,<ref name="Burnard-1997" /> and crust = 3000.<ref name="Ballentine-2002b"/>