Extinct radionuclides Chronology of solar system formation

Extinct radionuclides Chronology of solar system formation 

There are several cases in Table 1 (those with half-lives less than 10 years) where the half-life of the parent isotope is so short that any that was incorporated into a rock at the time of formation of the solar system 4.5 Ga ago will have long since decayed away. However, the noble gas daughter isotopes may still be present, and can be used to deduce the very early history of the solar system. Freshly fallen meteorites do contain some of these short-lived radioactivities, as a result of bombardment by cosmic rays (Wider 

this volume). But ratios like Cl/Cl and resulting from cosmic ray 

Extinct radionuclides have a huge advantage in precision over long-lived radionuclides. For example, a change in a factor of two in the abundance of requires only one half-life, 15.7 Ma, while the same length of time will cause a change of less than 1% in the abundance of since it is only about 1% of a half-life. On the other hand, since the extinct radionuclide is, by definition, completely decayed away, it is necessary to determine its abundance at some particular time to determine ages, a problem for all extinct radionuclides. 

The relative amount of attention given to extinet radionuelides eompared to the Ar- 

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