Number 221 (Story #2), April 10, 1995 by Phillip F. Schewe and Ben Stein EARTH'S INNER CORE MAY BE A SINGLE IRON CRYSTAL. Furthermore, the inner core's magnetism might even influence the field shape we observe at the surface. Lars Stixrude of the University of Gottingen in Germany and Ronald Cohen of the Carnegie Institution of Washington have proposed a model in which the 2400-km inner core consists of an immense collection of hexagonal close-packed grains in a nearly perfect alignment. The fact that such a crystalline structure would be mechanically anisotropic (that is, its elastic properties would vary in different directions) could help to explain the puzzling observation that seismic waves take longer to propagate through the planet in the plane of the equator than they do along the spin axis. Some scientists have reservations about this model. For example, how would the inner core's magnetism work its way outward past the turbulent motion of the fluid outer core? (Science, 31 March 1995.)