The Core-Mantle Boundary; Our Ever Changing Earth; Special Editions; by Raymond Jeanloz and Thorne Lay; 8 Page(s)

About 2,900 kilometers away--less than three days' drive, if that were possible--lies Earth's most dramatic structure. Largely ignored in past research, the remote region between the lowermost mantle and the upper core is proving to be crucial in understanding the chemical and thermal evolution of the planet. No longer regarded as simply a contact delineating the liquid-iron outer core from the rocky mantle, the core-mantle region may actually be the most geologically active zone of Earth. Its features seem to have changed immensely during Earth's history, and its physical properties vary from place to place near the bottom surface of the mantle. In fact, the physical changes across the interface between the core and mantle are more pronounced than those across the planetary surface separating air and rock.

The strong heterogeneity of the core-mantle boundary region is thought to influence many global-scale geologic processes [see "The Earth's Mantle," by D. P. McKenzie; Scientific American, September 1983]. The dynamics of the zone affect the slight wobbling of Earth's axis of rotation and characteristics of the geomagnetic field. Variations in the core-mantle region also modulate the convection in Earth's mantle, which is responsible for the movement of continents and tectonic plates.