托福阅读素材：寒武纪大爆发(社会科学篇)

　　托福阅读素材社会科学篇：在短暂的1亿年地质学周期中，所有现代动物群(包括现在已经灭绝的生物)进化了。这次快速的动物起源和分化常常被称为“寒武纪大爆发”。新东方在线托福网为大家带来托福阅读素材：寒武纪大爆发(社会科学篇)，希望对大家托福备考有所帮助，更多精彩尽请关注新东方在线托福网!

　　今天分享给大家的是对TPO5 The Cambrian Explosion的文章详细分析。一起学习吧!

　　The Cambrian Explosion

　　寒武纪大爆发

　　1.The geologic timescale is marked by significant geologic and biological events, including the origin of Earth about 4.6 billion years ago, the origin of life about 3.5 billion years ago, the origin of eukaryotic life-forms (living things that have cells with true nuclei) about 1.5 billion years ago, and the origin of animals about 0.6 billion years ago. The last event marks the beginning of the Cambrian period. Animals originated relatively late in the history of Earth—in only the last 10 percent of Earth’s history. During a geologically brief 100-million-year period, all modern animal groups (along with other animals that are now extinct) evolved. This rapid origin and diversification of animals is often referred to as “the Cambrian explosion.”

　　段落架构：地质年代是由重大地质事件和生物事件标记的。最近的一个事件标志着寒武纪的开始。动物的起源相对处于地球历史的晚期——仅存在于地球历史时间的1∕10。在短暂的1亿年地质学周期中，所有现代动物群(包括现在已经灭绝的生物)进化了。这次快速的动物起源和分化常常被称为“寒武纪大爆发”。

　　2.Scientists have asked important questions about this explosion for more than a century. Why did it occur so late in the history of Earth? The origin of multicellular forms of life seems a relatively simple step compared to the origin of life itself. Why does the fossil record not document the series of evolutionary changes during the evolution of animals? Why did animal life evolve so quickly? Paleontologists continue to search the fossil record for answers to these questions.

　　段落架构：一个多世纪以来，科学家们对这次大爆发一直有疑惑。为什么它发生的得这么晚?多细胞生物的出现相对于生命的出现而言则是一次相对简单的进化。为什么化石没有记录下动物演化的一系列变化呢?为什么动物生命进化得如此迅速呢?古生物学家们仍旧在研究化石记录以期回答这些问题。

　　3.One interpretation regarding the absence of fossils during this important 100-million-year period is that early animals were soft bodied and simply did not fossilize. Fossilization of soft-bodied animals is less likely than fossilization of hard-bodied animals, but it does occur. Conditions that promote fossilization of soft-bodied animals include very rapid covering by sediments that create an environment that discourages decomposition. In fact, fossil beds containing soft-bodied animals have been known for many years.

　　段落架构：关于这重要的1亿年内化石的缺失，有一种解释是早期的动物都是软体动物，它们很难形成化石。

　　4.The Ediacara fossil formation, which contains the oldest known animal fossils, consists exclusively of soft-bodied forms. Although named after a site in Australia, the Ediacara formation is worldwide in distribution and dates to Precambrian times. This 700-million-year-old formation gives few clues to the origins of modern animals, however, because paleontologists believe it represents an evolutionary experiment that failed. It contains no ancestors of modern animal groups.

　　段落架构：含有最古老的动物化石的伊迪卡拉化石群就全部由软体动物化石组成。伊迪卡拉沉积层的分布却遍及世界各地，并且可以追溯到前寒武纪时期。这些7亿年前形成的地层为现代动物的起源提供了一些新的线索。因为古生物学家们认为它代表着一次失败的进化试验，其中并没有包含任何现代动物的祖先。

　　5.A slightly younger fossil formation containing animal remains is the Tommotian formation, named after a locale in Russia. It dates to the very early Cambrian period, and it also contains only soft-bodied forms. At one time, the animals present in these fossil beds were assigned to various modern animal groups, but most paleontologists now agree that all Tommotian fossils represent unique body forms that arose in the early Cambrian period and disappeared before the end of the period, leaving no descendants in modern animal groups.

　　段落架构：以俄罗斯的一处地名而命名的Tommotian是一层包含动物残骸的较年轻的化石层。它形成于寒武纪的早期，并且同样只含有软体动物化石。人们认为这些化石中的动物分化出了各种各样的现代动物，但是古生物学家们现在却认为，所有的Tommotian化石都仅代表在寒武纪初期出现但到寒武纪结束时就消失了的特别生物。所以它们没有在现在动物中留下后代。

　　6.A third fossil formation containing both soft-bodied and hard-bodied animals provides evidence of the result of the Cambrian explosion. This fossil formation, called the Burgess Shale, is in Yoho National Park in the Canadian Rocky Mountains of British Columbia. Shortly after the Cambrian explosion, mud slides rapidly buried thousands of marine animals under conditions that favored fossilization. These fossil beds provide evidence of about 32 modern animal groups, plus about 20 other animal body forms that are so different from any modern animals that they cannot be assigned to any one of the modern groups. These unassignable animals include a large swimming predator called Anomalocaris and a soft-bodied animal called Wiwaxia, which ate detritus or algae. The Burgess Shale formation also has fossils of many extinct representatives of modern animal groups. For example, a well-known Burgess Shale animal called Sidneyia is a representative of a previously unknown group of arthropods (a category of animals that includes insects, spiders, mites, and crabs).

　　段落架构：第三种化石层既包含了软体动物也包含了硬体动物，它为寒武纪大爆发提供了证据。这些化石层含有大约32种现代动物，还有大约20种与现在动物截然不同以至于不可能分类为任何一种现代动物的其他动物体。伯吉斯页岩化石群也含有很多现在已经灭绝了的动物化石。例如伯吉斯页岩化石群中的一种著名动物，Sidneyia，就是一种典型的以前还不为人知的节肢动物。

　　7.Fossil formations like the Burgess Shale show that evolution cannot always be thought of as a slow progression. The Cambrian explosion involved rapid evolutionary diversification, followed by the extinction of many unique animals. Why was this evolution so rapid? No one really knows. Many zoologists believe that it was because so many ecological niches were available with virtually no competition from existing species. Will zoologists ever know the evolutionary sequences in the Cambrian explosion? Perhaps another ancient fossil bed of soft-bodied animals from 600-million-year-old seas is awaiting discovery.

　　段落架构：像伯吉斯页岩化石群这样的化石层表明进化不能总是被认为是缓慢的过程。寒武纪大爆涉及到了快速的进化分化，接着就是很多独特动物的灭绝。为什么这种进化如此迅速呢?很多动物学家认为这是很多几乎没有任何竞争性物种的环境使然。

　　疑难词：

　　Explosion n. 爆炸;爆发

　　Timescale时标

　　Diversification n. 多样化;变化

　　Sediment n. 沉积;沉淀物

　　Assign vt. 分配;指派

　　Slide n. 滑动;幻灯片vt. 滑动

　　Await vt. 等候，等待