The evolution of the continental crust: the isotope legacy (lecture)

Joint Celebrity Lecture with Edinburgh Geological Society

The discovery of radioactivity changed our understanding of the thermal evolution of the Earth, and provided ways to determine the age of the Earth and time scales of geological change. Isotopes were first described by Soddy in 1913, and much later the high precision measurement of radiogenic isotope ratios markedly changed the study of the continental crust. The discussions shifted from the movement of continents, and how they once fitted together, to models for when and how the continents formed, and the evolution of the Earth’s crust and mantle. The continental crust is characterised by peaks in the distribution of U-Pb crystallization ages, and these coincide with the ages of super-continents. Such peaks may reflect periods of high magmatic activity or, as argued here, the preservation potential of magmatic rocks in different tectonic settings. The peaks marked times of increased preservation within the crust, rather than times of anomalously high volumes of magma generation. Even though <5% of present continental crust is older than 3 Ga, there is increasing evidence that ~60-70% of the present volume of the continental crust had been generated by that time.