新GRE阅读全真题：地球冷暖周期.

新GRE考试非常人性的一点，对于考题出的很严格，经过多次锤炼之后，能考验出考生们的水平。考生们可以根据题库的题目复习新GRE考试，下面就将新GRE阅读理解真题进行解析，为考生们彻底分析在GRE阅读中出现的真题，帮助考生们复习。

　　21. 地球冷暖周期通过石头含铁量推定 　　Recent studies of sediment in the North Atlantic’s deepwaters reveal possible cyclical patterns in the history of Earth’s climate. Therock fragments in these sediments are too large to have been transported thereby ocean currents; they must have reached their present locations by travelingin large icebergs that floated long distances from their point of origin boremelting. 　　Geologist Gerard Bond noticed that some of the sedimentgrains were stained with ironoxide, evidence that they originated in localeswhere glaciers had overrun outcrops of red sandstone. Bond’s detailed analysisof deep-water sediment cores showed changes in the mix of sediment sources overtime: the proportion of these red-stained grains fluctuated back and forth fromlows of 5 percent to highs of about 17 percent, and these fluctuations occurredin a nearly regular 1,500-year cycle. 　　Bond hypothesized that the alternating cycles might beevidence of changes in ocean-water circulation and therore in Earth’sclimate. He knew that the sources of the red-stained grains were generallycloser to the North Pole than were the places yielding a high proportion of“clean” grains. At certain times, apparently, more icebergs from the ArcticOcean in the far north were traveling south well into the North Atlantic boremelting and shedding their sediment. Ocean waters are constantly moving, andwater temperature is both a cause and an fect of this movement. As watercools, it becomes denser and sinks to the ocean’s bottom. During some periods,the bottom layer of the world’s oceans comes from cold, dense water sinking inthe far North Atlantic. This causes the warm surface waters of the Gulf Streamto be pulled northward. Bond realized that during such periods, the influx ofthese warm surface waters into northern regions could cause a large proportionof the icebergs that bear red grains to melt bore traveling very far into theNorth Atlantic. But sometimes the ocean’s dynamic changes, and waters from theGulf Stream do not travel northward in this way. During these periods, surfacewaters in the North Atlantic would generally be colder, permitting icebergsbearing red-stained grains to travel farther south in the North Atlantic boremelting and depositing their sediment. 　　The onset of the so-called Little Ice Age (1300-1860),which followed the Medieval Warm Period of the eighth through tenth centuries,may represent the most recent time that the ocean’sdynamic changed in this way. If ongoing climate-history studies support Bond’shypothesis of 1,500-year cycles, scientists may establish a major natural rhythmin Earth’s temperatures that could then be extrapolated into the future.Because the midpoint of the Medieval Warm Period was about A.D. 850, anextension of Bond’s cycles would place the midpoint of the next warm intervalin the twenty-fourth century. 　　21.1. According to the passage, which of the following istrue of the rock fragments contained in the sediments studied by Bond? 　　A. The majority of them are composed of red sandstone. 　　B. They must have reached their present location over 1,500 years ago. 　　C. They were carried byicebergs to their present location. 　　D. Most of them were carried to their present location during a warm period inEarth’s climatic history. 　　E. They are unlikely to have been carried to their present location during theLittle Ice Age. 　　21.2. In the final paragraph of the passage (lines 27-33),the author is concerned primarily with 　　A. answering a question about Earth’s climatic history 　　B. pointing out a potential flaw in Bond’s hypothesis 　　C. suggesting a new focus for the study of ocean sediments 　　D. tracing the general history of Earth’s climate 　　E. discussing possibleimplications of Bond’s hypothesis 　　21.3. According to the passage, Bond hypothesized that whichof the following circumstances would allow red-stained sediment grains to reachmore southerly latitudes? 　　A. Warm waters being pulled northward from the GulfStream 　　B. Climatic conditions causing icebergs to melt relatively quickly 　　C. Icebergs containing a higher proportion of iron oxide than usual 　　D. The formation of more icebergs than usual in the far north 　　E. The presence of coldsurface waters in the North Atlantic 　　21.4. It can be inferred from the passage that in sedimentcores from the North Atlantic’s deep waters, the portions that correspond tothe Little Ice Age 　　A.. differ very little in composition from theportions that correspond to the Medieval Warm Period 　　B. fluctuate significantly in composition between the portions corresponding tothe 1300s and the portions corresponding to the 1700s 　　C. would be likely tocontain a proportion of red-stained grains closer to 17 percent than to 5percent 　　D. show a much higher proportion of red-stained grains in cores extracted fromthe far north of the North Atlantic than in cores extracted from further south 　　E. were formed in part as 　　答案：CEEC 　　以上就是新GRE阅读全真题，希望考生们通过对GRE阅读理解真题的复习，对于考试就会有更大的把握。在这里澳际教育预祝考生们取得理想成绩，达成留学梦想，更多关于新GRE阅读方面的经验请关注澳际教育。