For those inclined to gamble with disaster, nature offers plenty of prospects. Just ask the dinosaurs.
On Feb. 15, 2013, a fireball streaked across the sky over Chelyabinsk, Russia and exploded in a window-shattering airburst. It was nearly a disaster: A ground strike might have killed tens of thousands of people [source: Kaku]. Regardless, the event proved that Earth's game of asteroid Russian roulette is far from over.
Scant hours after the event, a space rock three times larger than Chelyabinsk's threaded the space between Earth and its artificial satellites. Had this city-killer struck a densely populated location like New York, it would have destroyed midtown instantly, blasted down surrounding skyscrapers and rained firestorm-spawning meteors for hours. Short-term death tolls might have reached the millions [source: Kaku].
Of course, water covers 71 percent of Earth, and many large inland regions remain sparsely populated. Thus, in the rare case that such a massive rock actually hit Earth, it would stand a small chance of striking a population center. But a nation-wrecker or even a planet-killer could come knocking someday, perhaps sooner than we'd like to think.
Take Apophis, an apartment-building-size asteroid due to kiss our atmosphere in 2029 and possibly smack right into us on its 2036 return trip. Astronomers are bullish that it won't, but if it does it will pack the wallop of a 300-megaton atom bomb, to say nothing of the ensuing fires, disruption of solar energy and famine [source: Kaku].