英语听力:探索发现 2014-06-29 BBC 地平线:陨石的真相-21(在线收听

 Comparing the effects of an airburst with a ground strike, it seems the Chelyabinsk got away lightly. It’s estimated that the largest piece to hit the ground weighed 500 kilos, a fraction of the asteroid’s original mass of 7,000 tonnes. 

 
Now if a piece of rock that big had hit that area of Russia, it would have produced a huge impact crater. Then that kinetic energy is then delivered into the ground and we see things like seismic shock. So, you get … people would feel earthquakes on the ground.
 
So the fact that it was an airburst actually limited the consequences for the people on the ground. So, yes, still quite dramatic, still, you know, obviously, causing injuries. But it could have been a lot worse, had it survived down to ground.
 
Ground strikes are amongst the most destructive natural hazards we know of. When viewed from space, Earth’s encounters with giant asteroids in its deep history are revealed. And there is evidence from our planet’s past of a truly devastating meteorite strike that decisively altered the course of life on Earth.   
 
Today millions of years after the impact, the evidence for that crater is well hidden. This is a gateway to the cenotes, the unique cave system of Mexico’s Yucatan Peninsula.
  原文地址:http://www.tingroom.com/lesson/yytltsfx/2014/273550.html