ABSTRACT
The Earth gives the impression that it is dependably constant. Over the time scale of a human lifetime, little seems to change, as John Burroughs noted when he wrote of “the unshaken permanence of the hills” of Ireland (John Burroughs 1875, Winter Sunshine, vol. II). The reality, however, is quite contrary to that experience. Every cubic centimeter of the Earth is in motion, and has been since the Earth was formed four and a half billion years ago. Indeed, the Earth is a profoundly dynamic entity. On the time scale of seconds earthquakes jar the Earth, over the time span of a few years volcanoes appear and grow, over millenia landscapes slowly evolve, and over millions of years the continents rearrange themselves on the planet’s surface.
