From layer cake to complexity; 50 years of geophysical investigations of the Earth

Geophysical observations of earth structure, kinematics, and dynamics have served as a core driver in the development of our current understanding of how the Earth evolves. They have provided essential insights that inform our ability to mitigate its hazards and effectively utilize its critical resources. Since the 1960s, when geophysical measurements played a central role in establishing the plate tectonics paradigm, geophysical techniques have become an increasingly sophisticated mainstay in our scientific tool kit for addressing a wide range of scientific and societal needs. From detailing the complex structural and compositional heterogeneities of the Earth's lithosphere and mantle to monitoring the tectonic processes that shape the Earth's surface and deep interior, from finding and monitoring the extraction of critical natural resources that are increasingly rare to real time warning systems that can provide life-saving alerts of tsunami and seismic shaking, geophysics continues to play an increasingly important role in our lives. The myriad ways in which geophysics has revolutionized our understanding of our planet, from core to ionosphere, are too vast to properly represent in any single review. Presented here are selected highlights from the myriad geophysical investigations of the solid Earth over the past 50 years. In an attempt to set some defensible boundaries, and with some consideration for the patience of the reader, I made some relatively arbitrary choices on field boundaries. Gravity, for example, has seen a dramatic resurgence due in part to advances such as satellite gravimetry (e.g., GRACE [Gravity Recovery and Climate Experiment]), but I chose to defer that to the realm of geodesy, along with GPS and InSAR (interferometric synthetic aperture radar). Slow earthquakes and episodic slip and tremor are also clearly important new phenomena for geophysical study, but to my mind they are more appropriately considered as tectonic developments. However, I trust the selected examples provided are representative of the impressive past impact and the exceptional future promise of the field of geophysics as a whole.