Earths Inner Core
Scientists have long struggled to understand what lies at the planets center. Direct observation of its center is impossible, so researchers must to other evidence.
In 1889, a German scientist detected a severe earthquake in Japan. Geophysicists concluded that shock waves jolts from one side of Earth through the center to the other side. Then in 1936, Danish geophysicist Inge Lehmann studied the waves to determine that within Earths core of molten iron lies a solid inner core - but that core was made of eluded her. Other geophysicists quickly determined that Lehmanns inner core was composed mostly iron. Since then, Lehmanns discovery has conventional Earth science.
But now scientists are challenging traditional theory with new and radical . For example, Earths center could actually contain an inner core within the inner core, claim Ishii and colleague Adam Dziewonski.
Analyzing hundreds of thousands of earthquake wave , they maintain that the inner core has at its heart a tiny, even more solid sphere . This sphere may be the oldest fossil from the formation of Earth, says Dziewonski.
Dziewonski and Ishii speculate that shortly Earth formed around 4.8 billion years ago, a giant asteroid smashed into the young planet and nearly melted it. But Earths center didnt quite melt; it mass as the planet cooled. The core within a core may be the kernel that endured. Its presence could change our basic ideas about the of the planet, Dziewonski says.
Dziewonskis idea is tame compared to the theories of independent geophysicist J. Marvin Herndon. Earths inner core is made not of iron, he claims, but a of nickel and silicon. Herndon has a truly revolutionary notion: Within the nickel silicide inner core is also an inner inner core - an 8 km-wide ball of the element uranium. Uranium is radioactive. Herndon thinks the uranium releases heat energy as its atoms fission-split and crash into one another in a chain reaction. In other words, we may live on top of a gigantic, natural nuclear power plant.
1 A try B leave C turn D point
2 A create B receive C feel D overcome
3 A work B solution C job D patterns
4 A whether B what C why D how
5 A from B within C of D to
6 A followed B dominated C restored D opposed
7 A ideas B demands C phenomena D movements
8 A things B acts C methods D records
9 A taken B benefited C left D kept
10 A after B before C since D when
11 A expanded B modified C gained D melted
12 A size B origin C structure D shape
13 A radical B traditional C classical D conventional
14 A system B copy C model D compound
15 A charge B last C experience D show
参考答案:
1. C 2. A 3. D 4. B 5. C
6. B 7. A 8. D 9. C 10. A
11. C 12. B 13. A 14. D 15. C
雅思考试学习策略笔记
雅思考试阅读8分牛人分享备考心得与建议
怎样写十篇作文搞定雅思写作7分
与“鸭子”搏斗--我的漫漫雅思之路
雅思听力解题三步骤流程详解
雅思大作文写作技巧及注意事项
雅思A类写作11个常见题材总结推荐
考友经验:高手谈雅思
菜鸟三次考雅思的不同经历经验
四个月雅思从6分到7分的点滴感受
雅思备考经验-给复习时间少的朋友们
如何一个半月拿到雅思7分的成绩
北京考试雅思详细过程
提高面试英语有绝招
雅思考试归来谈雅思
坚持就是胜利--三考雅思终得7分
雅思8分高考状元英语学习秘诀
IELTS成绩单成功敲开美国高校大门经验谈
雅考阅读、听力考试8.5分经验分享
名师指点雅思:先写小作文好处更多
关于雅思考试的一些实实在在的建议
雅思作文高分是如何炼成的
速提雅思有窍门
雅思7分经验谈:我进行雅思复习的三个阶段
雅思考试总结(no pain,no gain)
希望大家引以为鉴--雅思考试失败的经历
考试心得:高二女生第1次考雅思7.5分
大一女生半年复习雅思6.5分经验谈
我与雅思的第一次亲密接触
北京雅思听力考试考生回忆
| 不限 |
| 英语教案 |
| 英语课件 |
| 英语试题 |
| 不限 |
| 不限 |
| 上册 |
| 下册 |
| 不限 |