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Most climatologists believe that ice ages have occurred in cycles in part because Earth sways while orbiting the Sun, causing fluctuations in the intensity of sunlight reaching the Northern Hemisphere. This theory, proposed by the astronomer Milutin Milankovitch, gained acceptance in the 1980's after the oceanographer John Imbrie discovered supporting evidence in oxygen isotopes contained in shells deposited many thousands of years ago in ocean sediments.
A new study, however, suggests that ancient climates warmed and cooled independently of the Milankovitch orbital cycles. In a study of mineral calcite taken from the walls of Devil's Hole, a deep, freshwater-filled fissure in the Nevada desert, the geochemist Isaac Winograd analyzed the rate of decay of uranium into thorium and determined that the Devil's Hole data differ significantly from the ocean sediment data, suggesting that warm periods between ice ages lasted twice as long as previously thought. Based on his data, Winograd concluded that ice ages waxed and waned due to complex interactions among oceans, ice sheets, and atmosphere.
Some scientists believe that Winograd's data must be wrong. Imbrie, however, while asserting the correctness of the Milankovitch theory, suggests that the studies' different data concerning climate change may be due to geographical variations in climate and differences between marine and freshwater studies.
1.The passage suggests that the evidence discovered by Imbrie supports which of the following conclusions? A. Fluctuations in Earth's position as it orbits the Sun have resulted in the occurrence of ice ages. B. The atmosphere and the oceans both play a role in determining when an ice age will end. C. The reliability of data on oxygen isotopes found in shells from ocean sediments is questionable. D. Milankovitch did not consider sufficiently the differences between marine and freshwater environments when developing his theory of ice age cycles. E. Climates on Earth many thousands of years ago became warmer and cooler independently of Earth's orbital cycles.
2.According to the passage, Milankovitch's theory was not widely subscribed to by scientists prior to a study of which of the following? A. Oxygen isotopes in shell deposits B. Mineral calcite in a freshwater fissure C. Geographical variations in climate D. The rate at which uranium decays into thorium E. The interaction among the atmosphere, oceans, and ice sheets
3.The primary purpose of the passage is to A. criticize the methodology of a scientist's research B. report evidence that challenges a geochemist's theory C. explain why a widely accepted theory about ancient climates was abandoned D. describe some recent research on ice age cycles E. propose an innovative explanation for variations in oceanographic data
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发表于 2021-5-8 14:47:16
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