机经真题 1 Passage 1

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Dating the Arrival of Humans in North America

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According to paragraph 4, which of the following is NOT true about the slightly different varieties of stone hunting points found in some localities?

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  • A
    Radiocarbon dating revealed that they were several hundred years older than Folsom points.
  • B
    They appeared in layers that were beneath the layers containing Folsom points.
  • C
    They were regional variations of Folsom points.
  • D
    They were produced by a culture distinct from the one first identified in Folsom, New Mexico.
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正确答案: C

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  • Developed in the mid-twentieth century by Willard Libby and Jim Arnold, radiocarbon dating (used for dating organic materials) brought the chronology of North American prehistory into sharp focus. The method provided accurate ages for the deposits of organic material left behind by the last great ice sheets that covered the continent during the Pleistocene Ice Age that began approximately 1.6 million years ago. One such deposit was determined to be 11,400 years old. Radiocarbon was also used to date the traces (indications of their presence) left by America's earliest human inhabitants, enabling scientists to map out the movements of people and glaciers and to investigate the interrelationships between the two. Libby's first attempts to analyze an ancient North American site included what archaeologists call the Folsom culture.



    Folsom is a small town in northeastern New Mexico. In 1926-1927, arrowhead-like stone points were found there, mixed together with bones from a now-extinct type of bison, a discovery that caused great excitement because it placed humans in New Mexico during the last glacial period. when bison were abundant. Beyond that general observation, however, there was no way to date the site. Eventually, additional "Folsom" sites were discovered in other regions, all characterized by the same distinctive stone points. A few of these were in places that could be correlated with specific glacial deposits, which, through a fairly weak line of reasoning, were thought to be between 10,000 and 25,000 years old. Most workers favored the older end of the range.



    Arnold and Libby included a charcoal sample linked to the Folsom culture in their first published list of radiocarbon dates. The result was a surprise: 4,283 +/- 250 years B.P. (before the present). This was clearly much younger than any of the earlier estimates suggested, and, if the date held up, it would mean that what appeared to be one of the oldest Native American cultures was actually quite recent. Although they were confident about their analysis procedures, Libby and Arnold were suspicious of the result and wondered if the sample had been contaminated with young carbon, or if there was some other difficulty they were unaware of. In the end it turned out to be a classic case of improper sampling, and an example of the importance of careful field documentation. When the charcoal was collected in 1933 (it had been stored away from then until the analysis), it appeared to be lying within a soil layer that contained both animal bones and the distinctive Folsom stone points. But the unexpectedly young age prompted reexamination of the site, and it was determined that the charcoal came from a channel that cut into and through the older layers. Although it appeared to be at the same level as the bones and stone points, it was actually much younger. Once this problem was recognized and new samples from this and other sites were analyzed, it became clear that the most reliable Folsom ages fell in the range of 10,000 to 11,000 B.P.



    However, it was also discovered that Folsom sites are not the oldest evidence for humans in North America. At some localities, slightly different varieties of stone hunting points occur; initially it was thought that these were simply regional variations, or perhaps weapons used for hunting different types of animals. But, in some places-notably at Clovis, New Mexico-they appear in layers that lie beneath the typical Folsom points. This indicated that they were older, and soon archaeologists began to distinguish between Clovis and Folsom cultures. Obviously, Clovis sites became another target for radiocarbon dating, and the results confirmed their antiquity. Clovis sites consistently gave dates that were a few hundred years older than those characterized by the Folsom artifacts, and there seemed to be little or no overlap between the two cultures.



    With these results, the radiocarbon dates of both glacial deposits and archaeological sites in North America seemed to be painting a consistent picture. As the last severe glaciation of the Pleistocene Ice Age lost strength, early people spread into the United States. Clovis people were the first widespread hunters, making distinctive stone points for their weapons and hunting large game such as mammoths. Within a few hundred years, however, a new culture appeared, making smaller and finer stone points and apparently taking over from its Clovis predecessors as the dominant hunters in North America.


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    A.正确。段落中提到:"Clovis sites consistently gave dates that were a few hundred years older than those characterized by the Folsom artifacts"Clovis维斯遗址的一贯测定年代比Folsom 文物的年代早几百年。与选项A句意相符。 

    B. 正确。段落中提到:"they appear in layers that lie beneath the typical Folsom points"它们出现在典型的Folsom 石器层下面的地层中。与选项B句意相符。 

    C. 不正确。段落明确指出,最初认为这些石器是区域变种,但考古学家后来区分出Clovis文化和Folsom文化:"initially it was thought that these were simply regional variations... But... they appear in layers that lie beneath the typical Folsom points... archaeologists began to distinguish between Clovis and Folsom cultures."最初人们认为这些石器只是区域变种……但是……它们出现在典型的 Folsom石器层下面的地层中……考古学家开始区分Clovis文化和 Folsom文化。与选项C它们是Folsom石器的区域变种是矛盾的。 

    D. 正确。段落中提到:"archaeologists began to distinguish between Clovis and Folsom cultures"考古学家开始区分Clovis文化和 Folsom文化。与选项D句意相符。 

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