Stop the Killer Space Rocks: Scientific American:

Stop the Killer Space Rocks: Scientific American:

SNIP:

At first glance, asteroids may seem like a distant threat. But the hazard is well documented, and the consequences could not be more severe. The history of life on Earth has been shaped by asteroid impacts. One million of them wider than 40 meters in diameter orbit the sun in our vicinity, by some estimates. An asteroid of that size struck Earth over Siberia in 1908 and laid waste an area 150 times larger than the Hiroshima atomic bomb did. The odds of a repeat in this century are about 50 percent. On the larger end, asteroids greater than about one kilometer across would have global effects that threaten human civilization.

FULL ARTICLE:

http://www.scientificamerican.com/article.cfm?id=stop-the-killer-rocks&WT.mc_id=SA_CAT_SPC_20111208

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