2021年1月9日托福阅读真题+题目+答案：Dating the Arrival of Humans in North America

2021年1月9日托福阅读真题+题目+答案：Dating the Arrival of Humans in North America

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.

1.According to paragraph 1, which of the following statements is true?

O The last Pleistocene ice sheet in America was 11 ,400 years old when it deposited its organic materials.

O The developers of radiocarbon dating analyzed materials from America's early inhabitants.

O The movements of America s earliest inhabitants began after the movements of the glaciers ended.

O Ice sheet deposits that covered the continent during the Pleistocene Ice Age destroyed valuable information about the Folsom culture.

Folsom is a small town in northeastern New Mexico. In 1926-27, 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.

2.Paragraph 2 suggests that which of the following facts was known before the 1926-27 discovery in Folsom, New Mexico?

O Early humans in North America hunted with arrowhead-like stones.

O Certain bison species disappeared because they were hunted to extinction.

O Humans lived in New Mexico during the last glacial period.

O Bison were common in North America during the last glacial period.

3.According to paragraph 2, why were sites discovered in other regions also called “Folsom" sites?

O Because these sites were all settled by people from Folsom, New Mexico

O Because these sites could be correlated with specific glacial deposits

O Because the stone points found at these sites resembled those from Folsom

O Because inhabitants of these sites also hunted bison

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 ones 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.⬛

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