托福阅读真题+题目+答案+译文：The Cambrian Explosion

托福阅读真题+题目+答案：The Cambrian Explosion

1. The earliest fossil evidence for eukaryotescomplex organisms whose cells contain a distinct nucleusdates to only about 1.2 billion years ago. The fossil record suggests that animal evolution progressed slowly, with relatively little change seen between fossils from 1.2 billion years ago and those from a half-billion years later. But then something quite dramatic happened as can be judged by the many different animal groups that suddenly appear in the fossil record.

最早的真核生物化石证明：早在12亿年前，这种复杂的有机体细胞中包含有明显的细胞核。化石记录表明，动物进化发展缓慢，从12亿年前的化石和之后5亿年的化石之间，我们只能看到相对来说微乎其微的变化。后来某种相当具有戏剧性的事情发生了，因为大量不同的动物种群突然出现在化石记录中。

2. Biologists classify animals according to their basic body plans. For example, the basic body plan shared by mammals and reptiles is fundamentally different from that of insects. Animals are grouped by body plan into what biologists call phyla. Mammals and reptiles both belong to the single phylum Chordata, which includes animals with internal skeletons. Insects, crabs, and spiders belong to the phylum Arthropoda, which contains animals with body features such as jointed legs, an external skeleton, and segmented bodies. Classifying animals into phyla is an ongoing project for biologists, but modern animals appear to comprise about 30 different phyla, each representing a different body plan.

生物学家根据动物的基本身体结构来对其进行分类。例如：哺乳动物和爬行动物所共有的基本身体结构特征在根本上就不同于昆虫类动物的。根据身体结构特征，动物被划归到一个类群，就是生物学家所称的“门”。哺乳动物和爬行动物同属于单一的脊索动物门：包括拥有内部骨骼的动物。昆虫、螃蟹和蜘蛛属于节肢动物门：包括拥有如具关节的附肢、外骨骼、和分段式身体等身体特征的动物。对于生物学家来说，尽管将动物分类划入门是一项不间断的项目，但是现代动物似乎仅由大约30个不同的门组成，每一个门都代表着一种不同的身体结构。

3. Remarkably, nearly all of these different body plans, plus a few others that have gone extinct, make their first known appearance in the geological record during a period spanning only about 40 million yearsless than about 1 percent of Earth's history. This remarkable flowering of animal diversity appears to have begun about 545 million years ago, which corresponds to the start of the Cambrian period. Hence it is called the Cambrian explosion。The fact that the Cambrian explosion marks the only major diversification of body plans in the geological record presents us with two important and related questions: Why, so long after the origin of eukaryotes, did the pace of evolution suddenly accelerate dramatically at the beginning of the Cambrian, and why hasn't there been another period of similarly explosive diversification since then。

值得注意的是，在已知最早的地质记录中，几乎所有这些不同的门，加上其他一些已经灭绝的，仅仅持续了大约4千万年的时间，不到地球历史的百分之一。大约在5亿4千5百万年，如百花争鸣般，举世瞩目的动物多样性开始出现，与寒武纪初期相对应。因此，这种现象被称作“寒武纪生命大爆发”(the Cambrian explosion )。在地质记录中，寒武纪(Cambrian)生命大爆发标志着动物身体结构唯一主要的多样化这一事实，将两个重要且相关的问题摆在我们面前：为什么在真核生物起源这么长时间以后，动物进化的速度在寒武纪初期突然显著提高;为什么没有另一个出现类似动物多样性大爆炸的时期出现。

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托福阅读真题题目：

1..Paragraph 1 implies which of the following about evolutionary change

A. Eukaryotes have a very slow rate of evolution.

B. The fossil record of evolutionary change is incomplete for the first half-billion years of animal evolution.

C. Evolution has not always proceeded at the same rate.

D. Evolutionary rates of change in animals were slowing down considerably before a dramatic reversal happened 1.2 billion years ago.

2..The word ongoing in the passage is closest in meaning to

A. uncertain

B. full-time

C. important

D. continuing

3..In paragraph 2, why does the author provide the information that Arthropoda represents animals with features like jointed legs, an external skeleton, and segmented body parts

A. To indicate basic physical differences among insects, crabs, and spiders

B. To illustrate the types of physical characteristics considered when classifying animals

C. To show the complexity of features that have evolved in organisms

D. To demonstrate that some phyla include a wider range of body plans than others do

4..The phrase corresponds to in the passage is closest in meaning to

A. causes

B. occurs before

C. differs from

D. matches

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