German scientist detected a severe earthquake in Japan
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
上班族的快速屠鸭路10个晚上拿下6.5
二战雅思6升7诀窍的分享
雅思7.5分考生分享高效备考的方法
雅思高分怪招:单词分类综合学习法(2)
从复习到考试
师傅领进门修行在个人
二战雅思口语折戟沉沙
雅思听力阅读8.5分考生心得不要抱有心理负担
谨记:背雅思单词不能脱离语境
雅思口语6分并不难发音是关键流利很重要
对付雅思考试中的生词可以用哪些手段
雅思单词备考高分规律总结
时隔两年再次烤鸭的G类雅思的技巧
突击半个月我的雅思也可以拿8分
雅思考试巧记单词之单词拆分法
高二学生的雅思成功经验的分享
如何巧破雅思考试单词5000大关
一战雅思8分备考经验和技巧攻略
雅思听力阅读双8.5考生学习的心得
16天备考雅思6.5分经验的总结
如何将雅思词汇融入到日常生活
看电影讲故事
雅思牛人分享20天突击备考的方法
在校大学生一月备战雅思拿下口语8.5
破除雅思背单词难的魔咒
非牛人分享雅思备考经历考试千万别马虎
三周备考拿下雅思8分经验
“四好”方法助提升
如何纠正雅思发音及提高听力的技巧
雅思考试背单词方法之谐音法
不限 |
英语教案 |
英语课件 |
英语试题 |
不限 |
不限 |
上册 |
下册 |
不限 |