Britannica
Sources used in this answer
How does a radioactive isotopeās half-life affect its usefulness for dating?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
geochronology
The steep walls of the Grand Canyon contain a number of layers of sedimentary rock laid down over millions of years. The lower formations belong to the early Precambrian age, while the upper layers are of the Paleozoic age. The line between the two sets of formations is called the Great Unconformity.
In geochronology, a radioactive isotopeās half-lifeāthe time required for half of the parent atoms in a sample to decay into daughter atomsāis the primary factor determining its suitability for dating specific materials and time ranges.12
The half-life dictates the "clock" speed of the isotope, which must be appropriate for the age of the sample being analyzed:
- Long half-lives: Isotopes with very long half-lives, such as uranium-238 (4.468 billion years), are essential for dating ancient rocks and minerals. Because they decay slowly, a measurable amount of parent material remains even after billions of years, allowing scientists to calculate the age of Earth's oldest formations.321
- Short half-lives: Isotopes with shorter half-lives are required for dating more recent geologic or archaeological events. For example, carbon-14 has a half-life of approximately 5,730 years, making it ideal for dating organic materials from the last 50,000 to 60,000 years. If an isotope's half-life is too short, it will have decayed completely before the sample can be dated; if it is too long, the amount of daughter product produced may be too small to measure accurately in a young sample.132
Choosing the correct isotope ensures that the ratio of parent to daughter atoms is within a range that can be precisely measured by instruments like a mass spectrometer.14