Scientists have long struggled to understand what lies at the planets center. Direct observation of its center is impossible, so researchers must (1) to other evidence.
In 1889, a German scientist detected a severe earthquake in Japan. Geophysicists concluded that shock waves (2) jolts (晃动) from one side of Earth through the center to the other side. Then in 1936, Danish geophysicist Inge Lehmann studied the waves (3) to determine that within Earths core of molten (熔化了的) iron lies a solid inner core - but (4) that core was made of eluded (难倒) her. Other geophysicists quickly determined that Lehmanns inner core was composed mostly (5) iron. Since then, Lehmanns discovery has (6) conventional Earth science.
But now scientists are challenging traditional theory with new and radical (7). 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 (8), they maintain that the inner core has at its heart a tiny, even more solid sphere (球体). This sphere may be the oldest fossil (9) from the formation of Earth, says Dziewonski.
Dziewonski and Ishii speculate that shortly (10) Earth formed around 4.8 billion years ago, a giant asteroid (小行星) smashed into the young planet and nearly melted it. But Earths center didnt quite melt; it (11) mass as the planet cooled. The core within a core may be the kernel (核心) that endured. Its presence could change our basic ideas about the (12) of the planet, Dziewonski says.
Dziewonskis idea is tame (温和的) compared to the (13) theories of independent geophysicist J. Marvin Herndon. Earths inner core is made not of iron, he claims, but a (14) of nickel and silicon. Herndon has a truly revolutionary notion: Within the nickel silicide (硅化物) 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 (15) 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
体坛英语资讯:Frenchman Bosse crowned mens 800m world champion (updated)
国际英语资讯:1 in 4 U.S. voters think Trumps dealings with Russia illegal during campaign: poll
国际英语资讯:France urges DRRK to comply with obligations, prevent further tensions
体坛英语资讯:Polands Wlodarczkyk completes hat trick of womens hammer throw world titles
国际英语资讯:Young versus old, new divide in Brexit Britain
国际英语资讯:Monsoon induced disasters kill over 30 in 2 days in Nepal
国际英语资讯:Britain denies agreeing to multi-billion under Brexit divorce bill
国际英语资讯:Sisi reiterates need for Qatar to respond to Arab quartets concerns
国际英语资讯:Irans parliament takes steps to counter U.S. pressures
国际英语资讯:Chinas Dalian Wanda Australian operations not for sale: Aussie chief
国际英语资讯:Opposition parties barred from elections in Venezuela
国际英语资讯:Egypts Sisi urges faster railway development to avoid deadly crashes
国际英语资讯:Spotlight: Trump intensifies attacks at McConnell over health care failure
国际英语资讯:Nearly 1.6 mln Ukrainians displaced as conflict enters 4th year: UNHCR
国际英语资讯:Commentary: Britain takes step to protect personal data in digital era
国际英语资讯:Kenyas Kenyatta wins re-election, pledges to unite nation
国际英语资讯:U.S. federal court rules in favor of Chinese businesswoman beaten by border agent in 2004
国际英语资讯:ASEAN foreign ministers commend Chinas regional role
国际英语资讯:Singapore launches Southeast Asias largest drone light show at National Day Parade
国际英语资讯:China continues to see slowdown in luxury goods spending: report
国际英语资讯:At least one dead in car crash after violent rally in Virginia, U.S.
国际英语资讯:Investigation reopens against Brazilian former president Lula
国际英语资讯:Venezuela rejects Trumps threats of violence
国际英语资讯:Merkel offers more money to tackle refugee crisis
国际英语资讯:Spotlight: Chinese Americans divided on Trumps new immigration bill
国际英语资讯:Syria urges UN to dissolve U.S.-led coalition over crimes against civilians
国际英语资讯:Iran adopts economic diplomacy as key foreign policy
体坛英语资讯:Ronaldinho sets condition for return to football
体坛英语资讯:Czech Spotakova lifts second javelin throw world title (update)
国际英语资讯:UN chief urges Venezuelans to ease tensions, engage in negotiations
不限 |
英语教案 |
英语课件 |
英语试题 |
不限 |
不限 |
上册 |
下册 |
不限 |