Impact!: The Threat of Comets and Asteroids

Not since Spengler has the end of civilization been threatened so often. Astronomer Verschuur may well be right to be so alarmist. In recent centuries, humans tended to see the probability of being hit by a substantial meteoroid as being so slight as to be negligible. But then we discovered that the moon's craters did not originate in extinct volcanoes but in impacts. At the beginning of this decade, it became widely accepted that the dinosaurs were wiped out as a result of impact, more precisely an impact that created Chicxulub Crater off the coast of the Yucatan. Groups like Spacewatch have been discovering new NEOs (Near-Earth Objects) at an impressive rate. Finally, in 1994, after some much-publicized dud comets, the many fragments of comet Shoemaker-Levy 9 slammed into Jupiter causing, among other things, a 10,000-kelvin fireball that flew outward at 38,000 mph. Recently, estimates of the size of the impactor (or impactors) that could destroy much of the world has been reduced as it has become clearer that the real damage would not be so much to the land as to the atmosphere. Verschuur would have been better off letting these facts speak for themselves. Instead, he spends much of the book talking about the history of uniformitarianism vs. catastrophism without giving lay readers enough help with the underlying differences between the two. And his excitable prose sometimes undermines the power of the fact (""`Wow!' I responded profoundly to illustrate how stunned I was."") Verschuur's tone is that of a prophet in the desert, warning of doom with a sometimes disturbing single-minded determination: ""On the morning of June 30, 1908, civilization may have suffered the worst piece of luck in its history,"" he says describing the meteoroid that flattened miles in a remote area of Siberia. ""Had the Tunguska object struck a large city, a million people or more might have perished, and the phenomenon would have raised everyone's awareness to the threat of comet impact."" (Sept.)