首页
登录
职称英语
Eight times within the past million years, something in the Earth’s climatic
Eight times within the past million years, something in the Earth’s climatic
游客
2025-04-16
26
管理
问题
Eight times within the past million years, something in the Earth’s climatic equation has changed, allowing snow in the mountains and the northern latitudes to accumulate from one season to the next instead of melting away. Each time, the enormous ice sheets resulting from this continual buildup lasted tens of thousands of years until the end of each particular glacial cycle brought a warmer, climate. Scientists speculated that these glacial cycles were ultimately driven by astronomical factor; slow, cyclic changes in the eccentricity of the Earth’s orbit and in the tilt and orientation of its spin axis. But up until around 30 years ago, the lack of an independent record of ice-age timing made the hypothesis untestable.
Then in the early 1950’s Emiliani produced the first complete record of the waxings and wanings of first glaciations. It came from a seemingly odd place, the seafloor. Single-cell marine organisms called "foraminifera" house themselves in shells made from calcium carbonate. When the foraminifera die, sink to the bottom, and become part of seafloor sediments, the carbonate of their shells preserves certain characteristics of the seawater they inhabited. In particular, the ratio of a heavy isotope of oxygen (oxygen -18) to ordinary oxygen (oxygen -16) in the carbonate preserves the ratio of the two oxygens in water molecules.
It is now understood that the ratio of oxygen isotopes reflects the proportion of the world’s water locked up in glaciers and ice sheets. A kind of meteorological distillation accounts for the link. Water molecules containing the heavier isotope tend to condense and fall as precipitation slightly sooner than molecules containing the lighter isotope. Hence, as water vapor evaporated from warm oceans moves away from its source, its oxygen - 18 returns more quickly to the oceans than does its oxygen - 16. What falls as snow on distant ice sheets and mountain glaciers is relatively depleted of oxygen -18. As the oxygen -18 - poor ice builds up, the oceans become relatively enriched in the isotope. The larger the ice sheets grow, the higher the proportion of oxygen -18 becomes in seawater — and hence in the sediments
Analyzing cores drilled from seafloor sediments, Emiliani found that the isotopic ratio rose and fell in rough accord with the Earth’s astronomical cycles. Since that pioneering observation, oxygenisotope measurements have been made on hundreds of cores. The combined record enables scientists to show that the record contains the very periodicities as the orbital processes. Over the past 800, 000 years, the global ice volume peaked every 100, 000 years, matching the period of the orbital eccentricity variation. In addition, " wrinkles" superposed on each cycle — small decreases or surges in ice volume — have come at intervals of roughly 23, 000 and 41, 000 years, in keeping with the precession and tilt frequencies of the Earth’s spin axis. [br] As pointed out in the text, the ratio of oxygen -18 to oxygen -16 in seafloor sediments and that of these isotopes locked in glaciers and ice-sheets are______
选项
A、irrelevant
B、correlated.
C、corresponding.
D、identical.
答案
B
解析
题干问:“这篇文章指出,氧18和氧16在海底沉淀物中的比例和这两种同位素在冰山和冰层中的比例是……”。按照对2、3自然段的深入分析,发现这两种比例是相关的。海底的氧18比较多,而冰山的氧16比较多。因此选项B“相关的”为正确选项。而选项A“不相关的”,选项C“一致的”和选项D“相同的”都不是本题干所要求的内容。
转载请注明原文地址:http://tihaiku.com/zcyy/4039744.html
相关试题推荐
Ayearagothefirmhada______lossof4.3milliondollarsor20centsashare
Eighttimeswithinthepastmillionyears,somethingintheEarth’sclimatic
Eighttimeswithinthepastmillionyears,somethingintheEarth’sclimatic
Eighttimeswithinthepastmillionyears,somethingintheEarth’sclimatic
"RefrigeratorproductioninChinajumpedfrom1.4millionunitsin1985to1
Hewas______inthestreetsoftheMexicancapitalbymorethanamillionpeople,
EvenifIwonamillion-dollarlottery,Iwouldcontinuetolive______.(中国科学院200
Asskiesfillwithmillionsofmigratingbirds,Europeanscientistssaytheseas
(中国矿业大学2010年试题)Morethan600milliongirlsliveinpovertyinthedevelopin
(中国矿业大学2010年试题)Morethan600milliongirlsliveinpovertyinthedevelopin
随机试题
Whatdoesthemanaskthewomanabout?[br][originaltext]MAExcuseme,howmuc
AsurveyhasshownthatAmericansbelieveKansasis______visitedbyforeigntour
说明:假设你是一家旅行社的经理李明。当地旅游职业学院外事办的王主任4月15日给你写信,询问能否考虑赞助他们将在6月举办的为期一周的艺术节。请给王主任写一封回信。
对关键复杂的墙板进行拆分,解决钢筋绑扎、顺序问题等,并对该部分进行施工图深化属于
耦合表示模块之间联系的程度。横块的耦合类型通常可分为7种。其中,一组模块通过参
A.碳酸酐酶 B.假性胆碱酯酶 C.两者均有 D.两者均无白细胞内存在(
对脑缺血具有较好疗效的二氢吡啶类钙离子通道阻滞剂是A.氨氯地平 B.尼群地平
下列哪项是肝性脑病灌肠的禁用溶液A.酸性溶液 B.高渗盐水 C.低渗盐水
在回购协议市场中,可以作为回购证券标的物的有()。A.国库券 B.商业票
银行承兑汇票的承兑银行,应当按照票面金额向出票人收取()的手续费。A:千分之一
最新回复
(
0
)