Une datation radiométrique (dite « par radiochronologie ») est une méthode de datation absolue utilisant la variation régulière au cours du temps de la proportion de radioisotopes dans certains corps.
La plus connue est sans doute la datation par le carbone 14, mais il en existe bien d'autres.
Because rubidium is concentrated in crustal rocks, the continents have a much higher abundance of the daughter isotope strontium-87 compared with the stable isotopes.
Rubidium is a relatively abundant trace element in Earth’s crust and can be found in many common rock-forming minerals in which it substitutes for the major element .
Concurrently, the crust will become enriched in Rb relative to Sr.
A brief introduction to the radiogenic relationship between Rb and Sr: Rubidium-87 decays to Strontium-87 by beta decay according to the following equation: The amount of 87Sr found in a sample at any time is determined by the decay constant of 87Rb, the initial amount of 87Sr in the sample, the time since the initial time and the ratio of Rb to Sr in the system. Where lambda is the decay constant and t is the age of the system.
Dissolved strontium in the oceans today has a value of 0.709 that is dependent on the relative input from the continents and the ridges.
In the geologic past, changes in the activity of these two sources produced varying Sr ratios over time.
Some background on Rubidium and Strontium: Rb is a highly incompatible element.