Radioactive Decay and Rock Ages

The question of the age of the Earth and the Universe was long the subject of contentious discussion. Towards the end of the eighteenth century, it began to be recognized that undisturbed sediment layers represent a time sequence. The significance of fossils for the identification of layers of the same age was also understood. However, it was Darwin’s evolution theory on the development of species that led to the linking of the relationship between species development and the chronostratigraphic succession of sedimentary rocks. Nevertheless, Darwin’s evolution theory only provided a very vague understanding of the necessary time spans. But it was only after the discovery of radioactivity that rocks could be dated by radioactive decay clocks. This chapter discusses a selection of such radiometric methods suitable for dating rocks in a great spectrum of different ages.