Are All Mass Extinctions Caused By Collision

All five major mass extinctions would turn out to have been caused by the same mechanism, an asteroid collision.' Luis Alvarez

In his 1983 talk at the National Academy of Sciences, Luis Alvarez left no doubt just how far he thought his theory extended. He did acknowledge that the prediction quoted in the epigraph had not yet been confirmed, but made it clear that he believed it eventually would be. If it were confirmed, then not only might the explanation of mass extinctions have been discovered, so might the driving force behind evolution itself. Though geology offers no Nobel prize, the discovery of a robust general theory for mass extinctions, and especially of one linking them to extraterrestrial causes, surely would rank as one of the great scientific accomplishments of the twentieth century and place its authors in Nobel territory.

Physicists, even more than other scientists, seek the explanation of more than individual phenomena—they want to uncover the grand unified theory that will explain how each of the fundamental physical forces arises and interacts. Einstein, for example, tried to show that both electromagnetism and gravity derived from the same fundamental "force field." He was unable to do so, nor has anyone been able to since. Few geologists have even tried to imagine an all-encompassing theory for the earth: What could the unifier possibly be for the complex and seemingly random set of processes that characterizes our planet? Yet, we must ask the question: What of impact? It first created the inner planets through accretion, then destroyed

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