Different Parent/Daughter pairs have different half lives.  Two groups of Parent/Daughter Isotopes are used in radiometric dating:

1.        Primordial isotopes– these radioactive isotopes have very long half-lives, and are part of the original material present when the solar system formed.

Parent/Daughter pair                     Half Life                                Material Used

Rubidium87-Strontium 87            48.8 billion years               igneous/metamorphic rocks

Potassium40-Argon40                      1.3 billion years               igneous/metamorphic rocks

Uranium 238-Lead 206                   4.6 billion years                igneous/metamorphic rocks

Uranium 235-Lead 207                   0.7 billion years                igneous/metamorphic rocks

2.       Cosmogenic isotopes-these radioactive isotopes have very short half-lives, and are made continuously in the upper atmosphere.

        Parent/Daughter pair                     Half Life                Material Used

        Carbon-14/Nitrogen-14                 5,730 years         organics