It has been twenty years since Luis Alvarez suggested that the dinosaurs were extinguished by a meteor impact that killed much of the life on earth. His evidence was in a thin layer of iridium-rich soil that corresponded with the extinction, and the fact that iridium is much more abundant in some meteors than it is on earth. Now there is chemical evidence that an even more violent collision with an exterrestrial object occured at the end of the Permian, about 250 million years ago. This time the evidence is in the form of buckyballs that enclose helium or argon atoms. It turns out that carbonaceous meteors are rich in fullerenes and that one can tell that the noble gases entrapped are from outer space because their isotope distributions are different from those found on earth. An explanatory article, "Whiff of Gas Points to Impact Mass Extinction" by Richard A. Kerr appears on pages 1469-1470 of the same issue.
Luann Becker, Robert J. Poreda, Andrew G. Hunt, Theodore Bunch, and Michael Rampino