In 1997, the geoscientist Brian Toon and colleagues found that a space rock half a mile wide would produce an explosion that releases the energy equivalent of up to 100,000 million tons （Mt） of TNT. And a meteorite a mile in diameter might send enough pulverized rock into the stratosphere to block out sun-light and cause global cooling. The object that killed off the dinosaurs was probably seven or eight miles wide，says Jay Melosh, a planetary physicist at Purdue University. Its impact would have ejected a dust smoke that spread clear around the planet and rained blazing-hot on to forests, igniting them. “The dinosaurs probably broiled to death,” he says. Such a collision today would kill billions of people. Those who didn’t perish in the initial blast or the fires that followed would face long odds of finding sustenance. “People are going to starve to death,” Toon says. Still, a few would likely weather the apocalyptic storm. For a collision to wipe out the human race altogether, Toon estimates it would take a 60-mile-wide meteorite. He says, “That would bum everybody to death.” 
【正确答案】：47.100,000 million tons of TNT 48.block out sun-light and cause global cooling 49.seven or eight miles wide 50. a dust smoke51.burning everybody to death.