Wiktionary
rubidium-strontium
n. (context attributive English) Designating a method of geological dating based on the relative amounts in rock of rubidium-87 and its beta-decay product, strontium-87.
Usage examples of "rubidium-strontium".
Other radioactive 'stopwatches', each with its own characteristic rate of slowing down, are the rubidium-strontium, and the uranium— thorium-lead watches.