Scheme depicting the idea of continental drift as envisioned by A. Snider-Pellegrini in 1858 (A). This concept was re-discovered and supported by empirical evidence by A. Wegener in 1929. Decades later, the theory of plate tectonics was deduced. Plate tectonics accounts for most of the planet's earthquakes, which may result in deep cracks in the Earth's surface (B) and the formation of mountains as a result of horizontal compression of the crust (C) [adapted from ref. 58 and from photographs of the US Geological Survey, 1938].