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1、官网网站： _1新新 SAT 官方指南阅读第二十篇全解析官方指南阅读第二十篇全解析This passage is adapted from Carolyn Gramling, “Source of Mysterious Medieval Eruption Identified.” 2013by American Association for the Advancement of Science.About 750 years ago, a powerful volcano erupted somewhere on Earth, kicking off acenturies-long cold
2、 snap known as the Little Ice Age. Identifying the volcano responsible has beentricky. That a powerful volcano erupted somewhere in the world, sometime in the Middle Ages, iswritten in polar ice cores in the form of layers of sulfate deposits and tiny shards of volcanic glass.These cores suggest tha
3、t the amount of sulfur the mystery volcano sent into the stratosphere put it5firmly among the ranks of the strongest climate-perturbing eruptions of the current geologicalepoch, the Holocene, a period that stretches from 10,000 years ago to the present. A haze ofstratospheric sulfur cools the climat
4、e by reflecting solar energy back into space.In 2012, a team of scientists led by geochemist Gifford Miller strengthened the link betweenthe mystery eruption and the onset of the Little Ice Age by using radiocarbon dating of dead plant10material from beneath the ice caps on Baffin Island and Iceland
5、, as well as ice and sediment coredata, to determine that the cold summers and ice growth began abruptly between 1275 and 1300C.E. (and became intensified between 1430 and 1455 C.E.).Such a sudden onset pointed to a huge volcanic eruption injecting sulfur into the stratosphereand starting the coolin
6、g. Subsequent, unusually large and frequent eruptions of other volcanoes, as15well as sea-ice/ocean feedbacks persisting long after the aerosols have been removed from the官网网站： _2atmosphere, may have prolonged the cooling through the 1700s. Volcanologist Franck Lavigneand colleagues now think theyve
7、 identified the volcano in question: Indonesias Samalas. Oneline of evidence, they note, is historical records. According to Babad Lombok, records of theisland written on palm leaves in Old Javanese, Samalas erupted catastrophically before the end of20the 13th century, devastating surrounding villag
8、esincluding Lomboks capital at the time,Pamatanwith ash and fast-moving sweeps of hot rock and gas called pyroclastic flows.The researchers then began to reconstruct the formation of the large, 800-meter-deep calderaa basin-shaped volcanic crater that now sits atop the volcano. They examined 130 out
9、crops onthe flanks of the volcano, exposing sequences of pumiceash hardened into rockand other25pyroclastic material. The volume of ash deposited, and the estimated height of the eruption plume(43 kilometers above sea level) put the eruptions magnitude at a minimum of 7 on the volcanicexplosivity in
10、dex (which has a scale of 1 to 8)making it one of the largest known in theHolocene.The team also performed radiocarbon analyses on carbonized tree trunks and branches buried30within the pyroclastic deposits to confirm the date of the eruption; it could not, they concluded,have happened before 1257 C
11、.E., and certainly happened in the 13th century.Its not a total surprise that an Indonesian volcano might be the source of the eruption, Millersays. “An equatorial eruption is more consistent with the apparent climate impacts.” And, he adds,with sulfate appearing in both polar ice capsArctic and Ant
12、arcticthere is “a strong consensus”35that this also supports an equatorial source.Another possible candidateboth in terms of timing and geographical locationisEcuadors Quilotoa, estimated to have last erupted between 1147 and 1320 C.E. But when官网网站： _3Lavignes team examined shards of volcanic glass
13、from this volcano, they found that they didntmatch the chemical composition of the glass found in polar ice cores, whereas the Samalas glass is40a much closer match. That, they suggest, further strengthens the case that Samalas was responsiblefor the medieval “year without summer” in 1258 C.E.官网网站：
14、_442、The main purpose of the passage is toA) describe periods in Earths recent geologic history.B) explain the methods scientists use in radiocarbon analysis.C) describe evidence linking the volcano Samalas to the Little Ice Age.D) explain how volcanic glass forms during volcanic eruptions.正确答案：C分析：
15、文中作者提出：750年前的一次火山爆发，导致了长达一百年的小冰河世纪。并且论述了科学家的研究是如何支持这样的结论的。43、Over the course of the passage, the focus shifts fromA) a criticism of a scientific model to a new theory.官网网站： _5B) a description of a recorded event to its likely cause.C) the use of ice core samples to a new method of measuring sulfates.D) the use of radiocarbon dating to an examination of volc
