Introduction to methods and applications of geochronology: A perspective on geological time

Since the 17th century, the geological sciences have transitioned from a mostly qualitative “order of operations” discipline to a fully quantitative scientific discipline. In order to properly contextualize the origin and evolution of the solid Earth, a firm understanding of physical time and how it can be measured is required. Geological philosophy primarily advanced through rock and mineral observations, experimentation, and the study of the fossil record, but it was the development of analytical geochronology that quantified the age of geological and extraterrestrial materials and constrained the rates of past geological processes. The ability to measure individual isotopes and isotopic ratios by fission track methods and mass spectrometry revealed the vastness of geological time and permitted the robust correlations between rock formations across the globe, the reconstruction of supercontinents, and provided temporal constraints on biological evolution and the longevity of ancient ecosystems. The development of whole rock, single crystal, and in situ methodologies enhanced the ability of geoscientists to push scientific boundaries in the investigation of deep time. The application of geochronological methods can now offer accurate and precise results at various scales that range from crystal growth rates to crustal growth rates. In this chapter, we provide a perspective on the concept of geological time, the development of analytical geochronology, and the application of instruments. It is intended that this chapter acts as the historic foundation to the subsequent chapters that provide greater insight and the scientific basis for methods and applications of analytical geochronology.