Here's a breakdown:
* Rb (Rubidium): This is a radioactive element that decays into Sr (Strontium) over time.
* Sr (Strontium): This is a stable element that is the product of Rb decay.
In Rb-Sr geochronology, the following principles are applied:
1. Radioactive decay: Rb-87 (a radioactive isotope of rubidium) decays to Sr-87 (a stable isotope of strontium) at a known rate. This decay rate is called the half-life, which for Rb-87 is 48.8 billion years.
2. Isotopic ratios: The initial ratio of Sr-87 to Sr-86 (a non-radiogenic isotope of strontium) is measured in the rock or mineral sample.
3. Time and decay: As time passes, the amount of Rb-87 decreases, and the amount of Sr-87 increases proportionally.
4. Isochron: By plotting the measured ratios of Sr-87/Sr-86 against Rb-87/Sr-86 for different minerals within the same rock, a straight line called an isochron can be produced. The slope of the isochron is related to the age of the sample.
In summary:
* Rb is the "parent" isotope that decays.
* Sr is the "daughter" isotope produced by Rb decay.
By measuring the relative abundance of these isotopes and their ratios in a sample, scientists can calculate the time elapsed since the rock or mineral formed, providing valuable insights into geological history.
