英语听力：探索发现 2013-02-08 猛玛象进城记 Mammoths to Manhattan—5

 But there is a problem with the idea that hunting caused the mass extinction¹. Mammoths were not the only animals to disappear. 

 

Camels survived for millions of years in North America, but disappeared around the same time as the mammoths. Wild horses first evolved here and became dominant² grazers. Yet they, too, vanished soon after the Ice Age ended. But there’s little evidence to suggest that humans hunted horses or camels. This seems to go against the hunting argument. 

 

So what else would have triggered such large-scale extinctions? 

 

The other major possibility is climate change. The end of the Ice Age was a turbulent, erratic³ period. In some areas, rain patterns were shifting, bringing moisture back to dry landscapes and turning grassland⁴ into forest.

 

Other regions of the continent were plunged⁵ into prolonged periods of draught⁶. For grazers such as horses, this led to a massive change in habitat, one they were not flexible enough to overcome. 

 

As the land dried out, many grass eaters disappeared. We may never know for certain what killed off most of the larger animals at the end of the Ice Age. We do know that there was a time of coincidence—people were arriving just as the climate was in a state of change. Both may have played their part. Whichever was responsible, more than 70 species vanished for good, but some large animals did survive and still live here today.

1 extinction   

n.熄灭，消亡，消灭，灭绝，绝种

参考例句：

• The plant is now in danger of extinction.这种植物现在有绝种的危险。
• The island's way of life is doomed to extinction.这个岛上的生活方式注定要消失。

2 dominant   

adj.支配的，统治的；占优势的；显性的；n.主因，要素，主要的人(或物)；显性基因

参考例句：

• The British were formerly dominant in India.英国人从前统治印度。
• She was a dominant figure in the French film industry.她在法国电影界是个举足轻重的人物。

3 erratic   

adj.古怪的，反复无常的，不稳定的

参考例句：

• The old man had always been cranky and erratic.那老头儿性情古怪,反复无常。
• The erratic fluctuation of market prices is in consequence of unstable economy.经济波动致使市场物价忽起忽落。

4 grassland   

n.牧场，草地，草原

参考例句：

• There is a reach of grassland in the distance.远处是连绵一片的草原。
• The snowstorm swept the vast expanse of grassland.暴风雪袭击了辽阔的草原。

5 plunged   

v.颠簸( plunge的过去式和过去分词 )；暴跌；骤降；突降

参考例句：

• The train derailed and plunged into the river. 火车脱轨栽进了河里。
• She lost her balance and plunged 100 feet to her death. 她没有站稳，从100英尺的高处跌下摔死了。

6 draught   

n.拉，牵引，拖；一网（饮，吸，阵)；顿服药量，通风；v.起草，设计

参考例句：

• He emptied his glass at one draught.他将杯中物一饮而尽。
• It's a pity the room has no north window and you don't get a draught.可惜这房间没北窗，没有过堂风。