How does a radioactive isotope's half-life affect its use in geochronology?

In geochronology, a radioactive isotope's half-life—the time required for half of the parent atoms to decay into daughter atoms—is the critical factor that determines the appropriate time range and material for radiometric dating.12

Because different isotopes decay at vastly different rates, scientists select specific "chronometers" based on the age of the sample being studied. The half-life dictates the utility of an isotope as follows:12

• Short half-lives: Isotopes with relatively short half-lives, such as carbon-14 (approximately 5,570 years), are used for dating younger, organic materials, typically spanning up to 50,000 years.12
• Long half-lives: Isotopes with very long half-lives, such as uranium-238 (about 4.5 billion years), are essential for dating ancient rocks and establishing the geologic time scale.12

For a dating method to be effective, the sample must contain enough remaining parent atoms to measure accurately, meaning the isotope's half-life must be compatible with the estimated age of the geologic material.3