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1、http:/托福听力 TPO24 原文 Lecture3下面就让小编来为大家介绍一下托福听力 TPO24 原文中 Lecture 3 的文本内容吧，大家要好好把握，这些都是非常有价值的材料，同时，大家也可以登录前程百利论坛进行 TPO 练习辅导，希望能够给准备托福听力的同学带来帮助。TPO 24 Lecture3-Archaeology (Megafauna in North America)Professor：Between 11,000 and 10,000 B.C.E., North America was populated by a widevariety of great beas
2、ts, like mammoth and mastodons, both elephant-like creatures withbig tusks, and camels, giant sloths, the list goes on. By about 10,000 B.C.E., all those giantcreatures, the Metgauna of North America were gone. We dont know exactly whathappened to them, but there are some theories.One theory is that
3、 they were hunted toextinction by humans. The humans who coexisted with these giant species in NorthAmerica at that time were what we today called the Clovis Peopple. And there is a Clovissite in a valley in southern California where the remains of thirteen mammoths were found.And spear points, tool
4、s for processing meat, and fire places.That would appear to be somepretty compelling evidences. Mammoth bones have also been found at some other Clovissites.But then at other Clovis sites, theres also a lot of evidence that the Clovis peoplemostly gather plants and hunted small game, like rabbits an
5、d wild turkeys. Also there areseveral places in North America where you have natural accumulations of mammoth bonesthat look very similar to the accumulations at the Clovis site, except theres no humandebris, where the mammoth almost certainly died as a result of some kind of naturaldisaster. So I t
6、hink it is quite likely that those thirteen mammoths in southern Californiahttp:/also died of natural causes, and that the Clovis people simply took advantage of thesituation. Um.OK. Thats the hunting theory.Now lets look at another theory, uh, an alternative to the hunting theory, the climatechange
7、 theory. At around 11,500 B.C.E.，the world was coming out of an Ice Age .And withthat came increased seasonality, that is, the summers became warmer, and the wintersactually became colder. These extreme shifts would have put a lot of stress on the bodiesof animals that were used to a more moderate r
8、ange of temperatures.But the mostimportant impact of this increased seasonality may very well have been its effect on thedistribution of plants.Today we take for granted that there horizontal bands of plantcommunities. In the far north, it is tundra, which gives way to forest as you movesouthward. A
9、nd even farther south, grasslands take over. But during the Ice Age, theseplant communities actually grew together, mixed with one another. So Ice Age animals hadaccess to many different types of plants, different types of food. But when the seasonsbecame more distinct, the plant communities were pu
10、lled apart, that meant, in any givenarea, there was less plant diversity. And as a result, uh, so the theory goes, the Ice Ageanimals that depended on plant diversity couldnt survive. And the great beasts were theones that needed the most diversity in their diet. Again, we have what at first seems l
11、ike apretty attractive theory, but then, how do you explain the fact that this has happenedbefore? You know, global cooling followed by global warming, and there was no extinctionthen.Uh, you know, I recently read an interesting article about an archaeologist who triedto solve this puzzle with the h
12、elp of his computer. What he did was, he wrote a computerhttp:/program to simulate what would happen to mammoth under certain conditions. Say, forexample, there is a drought for a couple of decades, or hunters are killing or five percent ofthe population, and so on. One thing he found was that human
13、s didnt necessarily have tokill these animals in great numbers in order to nudge them toward extinction. Thatsbecause very large animals have a slow rate of reproduction, so all you have to do isremove a few young females from the herd, and you can, fairly quickly, significantly reducethe population
14、. And then he came up with a scenario that combined some hunting byhumans with some environmental stress, and.Bang! The simulated mammoths wereextinct within decades.So it seems the mixture of hunting and climate change is a likelyscenario. Uh, of course, computer simulations are not a substitute fo
15、r hard evidence.教授：在公元前 11000 年到 10000 年前，北美洲生活着各种大型的生物，比如猛犸和乳齿象，两种都是象类的生物，都有巨大的长牙，驼峰和大地懒和其他特征。但是大约在公元前 10000年时，所有的巨型生物，北美的猛犸都消失了。我们不能确定到底发生了什么事情，但是对此有许多理论。一种理论是说他们被人类猎杀以至于灭绝了。当时在北美洲与这些巨型生物同时存在的是我们现在所说的克洛维斯人。 在南加利福尼亚的山谷中发现了一个克洛维斯遗址， 这里发现了 13 只猛犸象的遗迹，同时还发现了矛头，加工肉的工具和篝火。这看起来是十分令人信服的证据。在其他的克洛维斯遗址中也发现了猛
16、犸象的骨头。但是在其他的克洛维斯遗址中，也有不少证据证明克罗维斯人大部分是以采集植物和猎杀小型动物为生，如兔子和野驴。而且在南美的一些地方还发现了许多自然急剧的猛犸象的骨头，看起来与克洛维斯遗址中的一样，只不过没有人类的遗迹，看起来猛犸象像是死于某种自然灾害。所以我认为在南加利福尼亚克洛维斯遗址中发现的 13 据猛犸象的也有可能是死于自然灾害，而克洛维斯人只是坐享渔翁之利。嗯，这就是猎杀理论。现在我们来http:/讨论另一个理论，他是猎杀理论的一个可替代理论，气候变化理论。在公元前 11500 年前，地球走出了冰河世纪。随之而来的是季节性的增加，夏天变得更加温暖，而冬天则变得更加寒冷。这种极端的变化可能给一直处于气候变化不大的环境中的动物的体能带来了很大的压力。而其中最大的冲击可能是对植物分布的影响。现在我们认为植物的水平分布理所当然。最北面是冻土带，接下来往南是森林带。而到了最南边是草原带。但是在冰河世纪，这些不同的植物实际上是长在一起的，相互融合。所以冰河
