text: Isotopes with extremely long half-lives and their decay products can be used to study multi-million year processes, such as tectonics and extreme climate change. For example, in rubidium–strontium dating, the isotopic ratio of strontium (Sr/Sr) can be analyzed within ice cores to examine changes over the earths lifetime. Differences in this ratio within the ice core would indicate significant alterations in the earths geochemistry.