What drives the tectonic plates as they glide over the Earth's surface? Searching for an answer, scientists have probed our planet to its core. In this realm of unimaginably high temperatures and pressures, matter takes on new forms, and solid rock can behave like a fluid. As vast masses of rock flow slowly within the Earth, so the surface moves and changes. Gigantic plumes of hot material can well up from the depths, triggering huge volcanic eruptions and causing the crust to bulge and break. The result may be the splitting of a continent and the creation of a new ocean basin.

• Aubrey Manning