Editing Radiometric dating (section)

===The <sup>26</sup>Al – <sup>26</sup>Mg chronometer===
Another example of short-lived extinct radionuclide dating is the {{SimpleNuclide|Aluminium|26|link=yes}} – {{SimpleNuclide|Mg|26}} chronometer, which can be used to estimate the relative ages of [[chondrule]]s. {{SimpleNuclide|Al|26}} decays to {{SimpleNuclide|Mg|26}} with a [[half-life]] of 720 000 years. The dating is simply a question of finding the deviation from the [[natural abundance]] of {{SimpleNuclide|Mg|26}} (the product of {{SimpleNuclide|Al|26}} decay) in comparison with the ratio of the stable isotopes {{SimpleNuclide|Al|27}}/{{SimpleNuclide|Mg|24}}.<ref>{{Cite journal |journal=Press Abstracts from the Nineteenth Lunar and Planetary Science Conference |last1=Hutcheon |first1=I. D. |last2=Hutchison |first2=R. |last3=Wasserburg |first3=G. J. |date=1988-03-01 |title=Evidence of In-situ Decay of 26Al in a Semarkona Chondrule |url=https://ui.adsabs.harvard.edu/abs/1988LPICo.650...14H |volume=650 |pages=14|bibcode=1988LPICo.650...14H }}</ref>

The excess of {{SimpleNuclide|Mg|26}} (often designated {{SimpleNuclide|Mg|26}}*) is found by comparing the {{SimpleNuclide|Mg|26}}/{{SimpleNuclide|Mg|27}} ratio to that of other Solar System materials.<ref>Alexander N. Krot(2002) Dating the Earliest Solids in our Solar System, Hawai'i Institute of Geophysics and Planetology http://www.psrd.hawaii.edu/Sept02/isotopicAges.html.</ref>

The {{SimpleNuclide|Al|26}} – {{SimpleNuclide|Mg|26}} chronometer gives an estimate of the time period for formation of primitive meteorites of only a few million years (1.4 million years for Chondrule formation).<ref>Imke de Pater and Jack J. Lissauer: ''Planetary Sciences'', page 322. Cambridge University Press, 2001. {{ISBN|0-521-48219-4}}</ref>