很多考生会抱怨托福阅读时间不够，还没完全理解文章就做题，正确率不高。其实这是我们对托福阅读素材不熟悉造成的，下面小编整理了一下托福阅读考试最新的素材，希望能帮助大家更加快速高效的备考托福。

　　托福阅读素材：寒武纪大爆炸

　　内容回忆：

　　第 1 段讲了生物的进化一般都比较慢，但是有一段时期生物的进化突然变的很快;第 2 段讲到科学家通过动物的 basic body plan 来把动物分成不同的 phyla,这个分类现在还在进行中，目前总共有 30 个不同的 phyla。第 3 段讲到了寒武纪大爆发的来源，由于所有这 30 个不同的 phyla 同时出现在了地质记录中，且时间刚好发生在寒武纪初期，就命名为寒武纪大爆发。第 4 段由于寒武纪大爆发是地质记录中唯一的生物多样性同时出现，引出了两个问题：第一，为什么这个时候的生物进化发送的如此快速?第二，为什么地质历史上没有其他的类似的物种多样性的爆发?第 5 段讲到，寒武纪爆发的可能的因素有四个，讲了其中一个，寒武纪之前氧含量比现在低很多。第 6 段讲了第二个原因是由于气候变化。第 7 段讲了第三个因素是由于基因复杂性的进化。第 8 段讲了第四个因素是由于有效捕食者的缺失。第 9 段讲解了为什么地质历史上没有其他的类似的物种多样性的爆发的原因可能就是由于第 4 个因素。

　　参考阅读：TPO5-3:The Cambrian Explosion

　　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.”

　　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.

　　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.

　　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.

　　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.

　　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).

　　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.

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