首页
登录
职称英语
[originaltext] Good afternoon, folks. In today’s lecture, we talk about the
[originaltext] Good afternoon, folks. In today’s lecture, we talk about the
游客
2023-12-21
20
管理
问题
Good afternoon, folks. In today’s lecture, we talk about the dinosaurs. One of the greatest mysteries about the dinosaurs is why they died out suddenly at the end of the Cretaceous Period 65 million years ago. A number of theories have been suggested to account for this mass extinction. The most popular theory is that a comet or meteorite hit the Earth and exploded with a terrific force, throwing up a dust cloud that blocked out the sun. Suddenly, it gets cold everywhere, and everyone dies. Nevertheless, I think this theory doesn’t work. Because it completely ignores most of what is happening on land. If you want to study dinosaurs and understand them, you’ve got to think about frogs and turtles and salamanders and mammals, too. You can’t take dinosaurs out of context. All the big animals were dinosaurs; that’s true. But most animals aren’t big. Go to the Amazon rain forest, or even a forest in New Jersey, and you’ll find that most of the animals there are small. If you exploded a nuclear bomb right now over Brazil blocking the sunlight and chilling the Amazon rain forest, who would die first? The big deer and jaguars or the little frogs? Frogs should die first, because they are the most delicate creatures in any ecosystem; their blood is in intimate contact with the water they live in. Also, a tropical frog exposed to a chill can’t hibernate, so it dies. A big animal, such as a deer or elephant, can stand a major chill and can move to another area. But have you ever heard of frog extinctions at the end of the Cretaceous Period? No. That’s because no frogs died out. No turtles or salamanders died out. None of these delicate animals, with no defense at all against a sudden chill, died out. But dinosaurs—the biggest, most active animals that should take weeks to kill—did die. This is true of every major extinction that has ever hit the Earth. Not so long ago, there were woolly mammoths and saber-toothed cats in Chicago. There were beavers the size of Buicks all over North America. They disappeared about 10,000 years ago So you may ask: what caused those mass extinctions? Well, it is very hard to come up with a theory that will kill big animals and leave little ones alone. The one thing that would do it is disease. This is a theory developed by American paleontologist Henry Osborn in 1899. He pointed out that when big animals travel, they’ll spread dozens of diseases and disrupt the ecology. Whenever we humans have brought animals from one continent to another, bad things happen. Someone brought starlings from England to North America, and we have a starling problem. Introduce foreign animals and they run amuck. They do not have natural predators and also they spread disease. Whenever there was a mass extinction on land, there were land bridges connecting the continents and big animals moving across them. During most of the history of life, broad oceans have separated the continents. But, periodically, those ocean barriers get drained away and animals can move. Big animals travel very easily. Give an elephant a land bridge and the population will spread at least 1,600 kilometers in two years. Little animals don’t move nearly as fast. It takes a long time for the population of a snake, salamander, or frog to spread. Osborn pointed out that if big animals move across land bridges and start spreading, you’re going to have extinctions caused by disease or disruptions to the ecosystem. There is no way to prevent it. So I like Osborn’s theory. It’s based in ecological reality. We know that foreign animals always cause disaster.
Question No. 16 What is the most popular theory about the dinosaurs’ extinction?
Question No. 17 Why are frogs the most delicate creatures in an ecosystem?
Question No. 18 What is the theory developed by American paleontologist Henry Osborn in 1899?
Question No. 19 Which of the following is NOT regarded as a major extinction of species?
Question No. 20 According to the speaker, what is essential in the spread of diseases by big animals?
选项
A、Dinosaurs.
B、Mammoths.
C、Saber-toothed cats.
D、Tropical frogs.
答案
D
解析
转载请注明原文地址:https://tihaiku.com/zcyy/3293536.html
相关试题推荐
[originaltext]下面你将听到的是一段有关中国经济社会发展的讲话。中国的改革开放已经走过了26个年头。26年来,中国发生了翻天覆地的变化。
[originaltext]下面你将听到一段介绍北京申奥功臣何振梁的讲话。7月13日晚,在莫斯科国际贸易中心,当国际奥委会主席萨马兰奇宣布北京获得2
[originaltext]下面你将听到的是一段介绍美国著名导演斯皮尔伯格的讲话。StevenSpielberg’sfirstfilmswe
[originaltext]下面你将听到的是一段有关中国教育改革与发展的讲话。党的十一届三中全会以来,随着党和国家工作重点转移到以经济建设为中心。
[originaltext]下面你将听到的是一段有关海洋的讲话。海洋是全球生命支持系统的一个不可缺少的组成部分。海洋不仅是自然资源的宝库,同时也是我
[originaltext]下面你将听到的是一段有关矿产开发的讲话。中国经济高速发展,需要大量的矿产品及相关的能源与原材料加工制品。每年消耗的矿石量
[originaltext]下面你将听到的是一段有关国际局势的讲话。InthewakeoftheColdWar,theworldh
[originaltext]下面你将听到的是一段有关金融改革的讲话。我国金融改革的不断深化将为外资银行与中资银行的合作带来新的机遇。银监会鼓励外资银
[originaltext]下面你将听到的是一位中国官员在世界经济论坛年会上的一段讲话。主席先生,女士们、先生们:目前,国际形势正处于深刻变化之
[originaltext]下面你将听到的是一段有关美国银行在亚洲拓展金融业务的讲话。Ifyouthoughtmultimediawass
随机试题
Fewpeopleexpectluxurywhileflying,butthesedays,【T1】________.It’snot
WY250表示( )的液压型挖掘机。A.斗容为25m3 B.斗容为2.5m3
治疗咽喉肿痛,痰盛咳嗽,应选用的药物是( )。A.青黛 B.板蓝根 C.大
A.刺络拔罐法 B.三棱针法 C.毫针补法 D.毫针泻法 E.针灸并用法
终身学习是教师专业发展的持续动力。( )
(2017年真题)基金公司信息技术系统的内部控制具有非常重要的意义,必须遵守的原
肉桂药材的断面特征是A:红棕色,纤维性强B:外侧呈棕色而粗糙,内侧红棕色而油润
国家对直接从江河取水的,实行( )。A.取水许可制度 B.自由取水制度 C
商业银行监事会中外部监事的人数不得少于()。 A.2名B.3名C.
(2015年真题)根据物权法律制度的规定,下列关于更正登记与异议登记的表述中,正
最新回复
(
0
)