The Whole-Earth Syndrome
Richard Monastersky · Science News · 1988
T here's no buttered popcorn, no music to accent the images on screen. Nonetheless, a dozen geophysicists and a few reporters stand captivated before the color television monitor, as 2 billion years of drama unfold before their eyes. They are watching the newest earthscience video starring the continental plates, moving at a film speed of about 700 million years a minute. In real life, the continents move too slowly to provide entertaining viewing material. If pitted in a race against a growing fingernail, the continents would just about tie. But in the movie, it is possible to watch the plates through the eyes of an earth scientist, who is accustomed to letting the mind fly through billions of years in a blink. On screen, the continents drift about, floating raft-like on a partially melted portion of the earth's mantle. Driven by convection currents in the mantle, the individual pieces ram together to form supercontinents, then rip apart into smaller bodies that head toward opposite ends of the frame. The video, which played last month at the American Geophysical Union meeting in Baltimore, is really a computer simulation called Supercontinent Aggregation and Dispersal, created by Michael Gurnis and colleagues Bradford Hager and Arthur Raefsky of the California Institute of Technology in Pasadena. Gurnis developed the numerical model to study the interplay between the movement of the continents and the flow patterns of rock in the mantle. Although still a crude approximation of the real thing, the model successfully mimics many of the events from the earth's history, he reports in the April 21 NATURE. And so far, the reviews on the model have been mostly thumbs up. It's not the first simulation, but it's the closest approach yet to what are considered the conditions inside the earth, says Peter Olson, a geophysicist who works on numerical and physical simulations at Johns Hopkins University in Baltimore. While Gurnis' work marks a technical achievement in computer modeling, it also exemplifies a new conceptual movement among those seeking to understand the inside of the planet. Geophysicists are beginning to examine the interrelations among the different sections of the planet: the core, the mantle and the much smaller crust. In the past, most scientists viewed these as isolated entities, but it is now clear that the separate regions are engaged in a multichannelled conversation. Across major boundaries and thousands of kilometers, these sections exert profound effects on one another. More people now are starting to appreciate that you have to treat the earth as a system; you can't just look at a part of it, says Don L. Anderson, a seismologist at Caltech. Geomagnetic people [who study the earth's magnetic field] used to just look at the core and not worry about the mantle, but we know now that they are interconnected. Likewise, until recently, the interrelationship between the buoyant, continental lithosphere and the mantle had been ignored, except in a few older papers.