Precise Pb.E2.80.93Pb dating of meteorites Lead–lead dating

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pb–pb isochrons oldest known material in solar system.


chondrules , calcium–aluminium-rich inclusions (cais) spherical particles make chondritic meteorites , believed oldest objects in solar system. hence precise dating of these objects important constrain evolution of solar system , age of earth. u–pb dating method can yield precise ages solar-system objects due optimal half-life of u. however, absence of zircon or other uranium-rich minerals in chondrites, , presence of initial non-radiogenic pb (common pb), rules out direct use of u-pb concordia method. therefore, precise dating method these meteorites pb–pb method, allows correction common pb.


when abundance of pb relatively low, isotope has larger measurement errors other pb isotopes, leading strong correlation of errors between measured ratios. makes difficult determine analytical uncertainty on age. avoid problem, researchers developed ‘alternative pb–pb isochron diagram’ (see figure) reduced error correlation between measured ratios. in diagram pb/pb ratio (the reciprocal of normal ratio) plotted on x-axis, point on y axis (zero pb/pb) have infinitely radiogenic pb. ratio plotted on axis pb/pb ratio, corresponding slope of normal pb/pb isochron, yields age. accurate ages produced samples near y-axis, achieved step-wise leaching , analysis of samples.


previously, when applying alternative pb–pb ischron diagram, u/u isotope ratios assumed invariant among meteoritic material. however, has been shown u/u ratios variable among meteoritic material. accommodate this, u-corrected pb–pb dating analysis used generate ages oldest solid material in solar system using revised u/u value of 137.786 ± 0.013 represent mean u/u isotope ratio bulk inner solar system materials.


the result of u-corrected pb–pb dating has produced ages of 4567.35 ± 0.28 cais (a) , chondrules ages between 4564.71 ± 0.30 , 4567.32 ± 0.42 (b , c) (see figure). supports idea cais crystallization , chondrule formation occurred around same time during formation of solar system. however, chondrules continued form approximately 3 after cais. hence best age original formation of solar system 4567.7 my. date represents time of initiation of planetary accretion. successive collisions between accreted bodies led formation of larger , larger planetesimals, forming earth–moon system in giant impact event.


the age difference between cais , chondrules measured in these studies verifies chronology of solar system derived extinct short-lived nuclide methods such al-mg, improving our understanding of development of solar system , formation of earth.








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