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摘要
Most scientists now agree that some sixty-five million years ago, an immense comet slammed into the Yucatan, detonating a blast twenty million times more powerful than the largest hydrogen bomb, punching a hole ten miles deep in the earth. Trillions of tons of rock were vaporized and launched into the atmosphere. For a thousand miles in all directions, vegetation burst into flames. There were tremendous blast waves, searing winds, showers of molten matter from the sky, earthquakes, and a terrible darkness that cut out sunlight for a year, enveloping the planet in freezing cold. Thousands of species of plants and animals were obliterated, including the dinosaurs, some of which may have become extinct in a matter of hours. In Impact, Gerrit L. Verschuur offers an eye-opening look at such catastrophic collisions with our planet. Perhaps more important, he paints an unsettling portrait of the possibility of new collisions with earth, exploring potential threats to our planet and describing what scientists are doing right now to prepare for this awful possibility.
Every day something from space hits our planet, Verschuur reveals. In fact, about 10,000 tons of space debris fall to earth every year, mostly in meteoric form. The author recounts spectacular recent sightings, such as over Allende, Mexico, in 1969, when a fireball showered the region with four tons of fragments, and the twenty-six pound meteor that went through the trunk of a red Chevy Malibu in Peekskill, New York, in 1992 (the meteor was subsequently sold for $69,000 and the car itself fetched $10,000). But meteors are not the greatest threat to life on earth, the author points out. The major threats are asteroids and comets. The reader discovers that astronomers have located some 350 NEAs ("Near Earth Asteroids"), objects whose orbits cross the orbit of the earth, the largest of which are 1627 Ivar (6 kilometers wide) and 1580 Betula (8 kilometers). Indeed, we learn that in 1989, a bus-sized asteroid called Asclepius missed our planet by 650,000 kilometers (a mere six hours), and that in 1994 a sixty-foot object passed within 180,000 kilometers, half the distance to the moon. Comets, of course, are even more deadly. Verschuur provides a gripping description of the small comet that exploded in the atmosphere above the Tunguska River valley in Siberia, in 1908, in a blinding flash visible for several thousand miles (every tree within sixty miles of ground zero was flattened). He discusses Comet Swift-Tuttle--"the most dangerous object in the solar system"--a comet far larger than the one that killed off the dinosaurs, due to pass through earth's orbit in the year 2126. And he recounts the collision of Comet Shoemaker-Levy 9 with Jupiter in 1994, as some twenty cometary fragments struck the giant planet over the course of several days, casting titanic plumes out into space (when Fragment G hit, it outshone the planet on the infrared band, and left a dark area at the impact site larger than the Great Red Spot). In addition, the author describes the efforts of Spacewatch and other groups to locate NEAs, and evaluates the idea that comet and asteroid impacts have been an underrated factor in the evolution of life on earth.
Astronomer Herbert Howe observed in 1897: "While there are not definite data to reason from, it is believed that an encounter with the nucleus of one of the largest comets is not to be desired." As Verschuur shows in Impact, we now have substantial data with which to support Howe's tongue-in-cheek remark. Whether discussing monumental tsunamis or the innumerable comets in the Solar System, this book will enthrall anyone curious about outer space, remarkable natural phenomenon, or the future of the planet earth.
评论 (4)
出版社周刊评论
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.) (c) Copyright PWxyz, LLC. All rights reserved
Kirkus评论
Verschuur, an astronomer (Hidden Attraction, 1993), offers a detailed and alarming account of the meteors and comets that have struck the Earth in the past, with devastating consequences, and reminds us that such disasters are likely to reoccur. He begins his account in 1980 with the discovery of an anomalous concentration of the element iridium at the geological boundary between the Cretaceous and Tertiary eras--the point at which the dinosaurs became extinct. Rare on Earth, iridium is far more common in comets and meteors; this discovery led to the theory that a massive comet striking the earth with the impact of 20 million hydrogen bombs led to the death of the dinosaurs. At first reluctant to accept the concept, many geologists were eventually brought around by the discovery of a massive impact crater near Yucatán. Verschuur then examines both the geological and astronomical evidence for frequent large impacts: the presence of other craters on Earth (145 had been identified by 1995), the prevalence of craters on other bodies of the solar system, the large number of astronomical bodies in near-Earth orbits, historical accounts of comet or meteor impacts. Verschuur places great emphasis on the possibility of a large, devastating strike in the near future. He also gives particular attention to the consequences of an ocean impact (in fact, the most likely scenario), with huge tsunamis crashing hundreds of miles inland. And he considers courses of action we might take, emphasizing a program to detect (and possibly deflect) the menaces from space. Verschuur argues that we should seriously entertain the prospect of moving some of Earth's population off the planet, to allow the human race to survive an unpreventable large strike. Occasionally overblown, often jumpy in its organization, this is nonetheless a strong treatment of one of the key scientific discoveries of our time. (40 halftones, 3 linecuts, not seen)
Choice 评论
Several books on the possibility of collisions with asteroids and comets have appeared in the last few years. One of the first was Cosmic Catastrophes, by Clark R. Chapman and David Morrison (CH, Nov'89); following the cometary impact on Jupiter, several more appeared. Impact is different from Cosmic Catastrophes in that it is directed only at comets and asteroid collisions, and although it covers the 1994 impact on Jupiter, it does so in one chapter. Overall, the book is a treat to read: Verschuur has an engaging writing style, and in many places his book reads almost like a novel. He gives a down-to-earth, realistic assessment of the danger Earth faces from space. This view is quite different from that of only a few years ago, when it was believed that disastrous collisions only occurred every million years or so. The book is well researched and presents a lot of useful information. Verschuur is well qualified to write such a book; he wrote one on the same subject in 1978 (Cosmic Catastrophes, CH, Dec'78). This is not just an update of that book, however; so much has happened in the meantime, that it is a completely new book. Highly recommended. B. R. Parker Idaho State University
《图书馆杂志》(Library Journal )书评
Earth may not need a plan to counter an alien invasion, but its inhabitants would be wise to determine the extent of a more likely threat from outer space: the untold numbers of comets and asteroids hurling around the solar system, some of which are bound to hit home sooner or later. So warns astronomer and science writer Verschuur (Hidden Attraction, Oxford Univ., 1993), who insists on the need for a thorough census of large objects with earth-crossing orbits. Beginning with the reputed dinosaur-killing asteroids and ending with the Jupiter comet hits of 1994, Verschuur traces the geographical and historical evidence suggesting the role of such collisions in the earth's formation, the evolution of life, and even in the course of human civilization. He laments that our species has been slow to accept the reality of the situation despite having evolved to the point where we might actually be able to defend ourselves against future impacts. This interesting and accessible if somewhat repetitive book is recommended for public and academic libraries. [We are being bombarded not only by comets but also by books about them; see Duncan Steel's Rogue Asteroids and Doomsday Comets, LJ 5/1/95; John Lewis's Rain of Iron and Ice, LJ 1/96; and John and Mary Gribbin's Fire on Earth, LJ 6/1/96.Ed.]Patrick Dunn, East Tennessee State Univ. Lib., Johnson City (c) Copyright 2010. Library Journals LLC, a wholly owned subsidiary of Media Source, Inc. No redistribution permitted.