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
精选英语散文欣赏:一棵小苹果树
精选英语美文阅读:爱的奇迹 Keep on Singing
英语美文:艰难岁月也要满怀感恩之心(双语)
英语美文:生命这个奇迹
精选英语美文阅读:爱会伴随着度过一生
精选英语美文阅读:别让蜡烛熄灭
伤感美文:人生若只如初见
浪漫英文情书精选:Could This Be Real?这是真的吗?
英语标准美文85
精选英语美文阅读:生活的涟漪
英语名篇名段背诵精华20
26个英文字母蕴含的人生哲理
英语美文30篇系列之21
浪漫英文情书精选:My Everything我的一切
人生哲理:年轻无悔 别停下追寻梦想的脚步
英语晨读:忘忧树
英语美文:Keep on Singing
“母亲”这个伟大的职业(双语)
精选英语美文阅读::朋友的祈祷
英语名篇名段背诵精华27
诗歌:放慢你的舞步
英语晨读:潘多拉
浪漫英文情书精选:Keep You Forever永远温存着你
英语美文:越长大越孤独(双语)
最美的英文情诗:请允许我成为你的夏季
英语美文:一双丝袜(有声)
英语美文欣赏:A beautiful song
双语阅读:回家的感觉真好
双语美文精选:但愿人长久,千里共婵娟
精选英语美文阅读:被忽略的爱 Helpless love
不限 |
英语教案 |
英语课件 |
英语试题 |
不限 |
不限 |
上册 |
下册 |
不限 |