Development of this process was aided by German chemists Otto Hahn and Fritz Strassmann, who later went on to discover nuclear fission in December 1938.
The utility of the rubidium-strontium isotope system results from the fact that Sr with a half life of 48.8 billion years.
Relative age dating also means paying attention to crosscutting relationships.
Say for example that a volcanic dike, or a fault, cuts across several sedimentary layers, or maybe through another volcanic rock type.
In a way this field, called geochronology, is some of the purest detective work earth scientists do.