The earth's dynamic surface is divided into a dozen main crustal plates whose slipping and sliding unleash volcanoes, build mountain ranges and trigger earthquakes. But the workings of the inner world are invisible and frustratingly hard to decipher. Now Mark Richards of the University of California at Berkeley and Hans-Peter Bunge of Los Alamos National Laboratory have created computer simulations of the earth's interior that show in vivid detail the churning, convective processes that--literally--rock our world.
These images help to solve a long-standing question of geophysics. In the simplest earth models, each convective loop or "cell" is only about as wide as it is deep. That pattern would indicate that the largest of the plates should be about as wide as the depth of the earth's mantle, or about 3,000 kilometers. But the Pacific plate spans more than four times that distance. Richards and Bunge suspected that the models were ignoring a key factor: the way that the viscosity, or stickiness, of the hot-mantle rocks changes with depth.
The work of Richards and Bunge comes on the heels of a number of other breakthroughs in understanding the earth's deep insides--detailed models of the dynamo that drives the earth's magnetic field, for instance, and the discovery of the crystal structure and independent motion of the inner core. Armed with faster computers and more complete seismic data, geophysicists are making remarkable progress in unveiling the once secret realms beneath our feet.