The history of Earth is written on the great tablets of tectonic plates. The motions of plates shaped land masses, formed oceans, and created the varied climates and habitats that set the stage for evolution and the diversity of life. But this grand drama begins with a deep mystery: just when did th e continental and oceanic plates begin to drift? Did the lithosphere begin to move soon after the formation of Earth 4.5 billion years ago or only in the last billion years? ...read more read less