英语听力：探索发现 2012-11-02 美洲大平原 American Serengeti—3

搜索关注在线英语听力室公众号：tingroom，领取免费英语资料大礼包。

 

This was once a bear, but not like any bear in North America today. Claw marks gouged¹ into the cave wall showed the bear was not killed direct by the fall. It made a desperate attempt to climb back out. It was a short-faced bear, an ice age heavyweight. What else can we tell about it from its bones? Its weight was more than 700 kilos, twice that of a grizzly² bear today. Upright, it would’ve stood four meters tall. It was the largest flesh-eating mammal that ever walked the earth.

 

The Wyoming cave, appropriately christened natural trap, provides a unique window of the Ice Age. During its coldest era, much of North America was covered by huge ice sheets up to two miles thick, but as the continent began to warm, the ice sheets started shrinking. 

 

Corridors began to open up along the coast and through the mountains, letting people migrate south from Alaska for the first time. Before them lay the almost limitless great plains stretching all the way from the Rocky Mountains to the Mississippi River and beyond to Mexico.

 

Across this area, the shifting ice left deep scars on the land. They carved out thousands of lakes and ponds, and left the tapestry³ of streams and rivers that drained the plains.

分享到：