In the 7500 kilometers from its center to the fringes of its upper atmosphere, the Earth plays host to an array of dynamic processes, operating on a range of length and time scales. Those processes include the convective swirls and eddies of the liquid outer core, which give rise to the planet's magnetic field; the far slower churning of the mantle, which moves whole continents; the intricately coupled interplay of two vast heat reservoirs, the ocean and the atmosphere, which manifests its complexity in climatic oscillations such as El Niño; and the sometimes violent interactions of the outer atmosphere, the magnetosphere, and the solar wind, which create extraterrestrial storm systems that can perturb "space weather" for tens of Earth radii.

The 16 June 2000 Special Issue of Science looks at the state of the art in Earth systems research -- and, in particular, at how the combination of geophysical and geochemical approaches, as well as the application of sophisticated 3D numerical modeling, is allowing new insights on how the planet works. To point you toward some additional online resources, and to add historical perspective to the discussions in the Special Issue, we've prepared this Science Online supplement.

The Earth's dynamism is well represented on the World Wide Web, with rich data sources, reference models of the planet's physics and chemistry, and hundreds of sites with everything from primers on space weather to movies of annual ENSO sea surface temperature anomalies. We take a brief tour of some of our favorites.

The past quarter-century has seen an immense deepening in our understanding of basic Earth processes, an intellectual development documented through the years in the pages of Science. To supplement the reviews in the 16 June 2000 Special Issue, we've gathered together a sampling of earlier papers from Science on topics related to the themes of the Special Issue -- including some studies not previously available on Science Online.

Thanks to David Gillikin, Wendy Shank, and
Cadmus Press for their assistance with this project.

Questions? Get in touch with Stewart Wills.