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  3. 　　 Scientists have discovered that for the last 160,000 years, at least, there 　　has been a consistent relationship between

　　 Scientists have discovered that for the last 160,000 years, at least, there 　　has been a consistent relationship between

admin2004-12-30  64
问题 　　    Scientists have discovered that for the last 160,000 years, at least, there
　　has been a consistent relationship between the amount of carbon dioxide in the air
　　and the average temperature of the planet. The importance of carbon dioxide in
　　regulating the Earth’s temperature was confirmed by scientists working in eastern
(5) Antarctica. Drilling down into a glacier, they extracted a mile-long cylinder of ice
　　from the hole. The glacier had formed as layer upon layer of snow accumulated year
　　after year. Thus drilling into the ice was tantamount to drilling back through time.
　　The deepest sections of the core are composed of water that fell as snow 160,000 years
　　ago. Scientists in Grenoble, France, fractured portions of the core and
    temperature and of atmospheric
(10)measured the composition of ancient air released from bubbles in the ice. Instruments
　　were used to measure the ratio of certain isotopes in the frozen water to get an idea
　　of the prevailing atmospheric temperature at the time when that particular bit of
　　water became locked in the glacier. The result is a remarkable unbroken record of
(15)levels of carbon dioxide. Almost every time the chill of an ice age descended on the planet, carbon
　　dioxide levels dropped. When the global temperature dropped 9F (5℃), carbon dioxide levels
　　dropped to 190 parts per million or so. Generally, as each ice age ended and the Earth basked in a
　　warm interglacial period, carbon dioxide levels were around 280 parts per million. Through the
　　160,000 years of that ice
(20)record, the level of carbon dioxide in the atmosphere fluctuated between 190 and 280 parts per
　　million, but never rose much higher-until the industrial Revolution beginning in the eighteenth
　　century and continuing today. There is indirect evidence that the link between carbon dioxide levels
　　and global temperature change goes back much further than the glacial record. Carbon
(25)dioxide levels may have been much greater than the current concentration during the Carboniferous
　　period. 360 to 285 million years ago. The period was named for aprofusion of plant life whose
　　buried remains produced a large fraction of the coal deposits that am being brought to the surface
　　and burned today.
选项 A、Chemical causes of ice ages
B、Techniques for studying ancient layers of ice in glaciers
C、Evidence of a relationship between levels of carbon dioxide and global temperature
D、Effects of plant life on carbon dioxide levels in the atmosphere
答案C
解析
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