3.8.1.4
Uranium-lead dating determines the age of rocks over billions of years
Radioactive Decay & Half-Life — AQA A-Level Physics
- Uranium-238 decays through a chain of alpha and beta decays, ending at stable lead-206.
- U-238 has a half-lifeThe time taken for half the number of radioactive nuclei in a sample to decay, or for the activityThe number of nuclear decays per unit time. Measured in becquerels (Bq), where 1 Bq = 1 decay per second. to halve. of 4.5 billion years — suitable for geological timescales.
- Initially a rock contains only uranium. Over time, the ratio of Pb-206 to U-238 increases.
- Measuring this ratio allows the age of the rock to be determined.
- This method was crucial in establishing that the Earth is ~4.5 billion years old.