One of the main weaknesses of the environmental movement has been its unfortunate predilection for using doom-laden language and catastrophic superlatives to describe problems that are serious but not immediately disastrous. But one calamity that truly deserves such a description is almost never talked about. There are tens of millions of asteroids in the solar system, and several thousand move in orbits that take them close to Earth. Sooner or later, one of them is going to hit it.
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©NASA
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Several have done so in the past. Earth's active surface and enthusiastic weather conspire to scrub the tell-tale impact craters from the planet's surface relatively quickly, but the pockmarked surface of the moon - where such scars endure for much longer - testifies to the amount of rubble floating in the solar system. Earth's thick atmosphere makes it better protected than the moon: asteroids smaller than about 35 metres (115 feet) across will burn up before hitting its surface. Nevertheless, plenty of craters exist. The Earth Impact Database in Canada lists more than 170.
Comment: Does it add up for you, readers?