学位英语

Earth’s Inner Core

Scientists have long struggled to understand what lies at the planet’s center, Direct

observation of its center is impossible，so researchers must_____(51)to other evidence.

In 1889，a German scientist detected a severe earthquake in Japan.Geophysicists concluded

that shock waves_____(52)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______(53)

to determine that within Earth’s core of molten(熔化了的)iron lies a solid inner core-but_____

(54)that core was made of eluded(难倒)her.Other geophysicists quickly

determined that Lehmann’s inner core was composed mostly_____(55)iron. Since then，

Lehmann’s discovery has_____(56)conventional Earth science.

But now scientists are challenging traditional theory with new and radical _____(57)

For example，Earth’s center could actually contain an“inner core within the inner core，claim Ishii and colleague Adam Dziewonski.

Analyzing hundreds of thousands of earthquake wave _____(58),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____(59)from the formation of Earth，”says Dziewonski.

Dziewonski and Ishii speculate that shortly_____(60) Earth formed around 4.8billion years ago，a giant asteroid(小行星)smashed into the young planet and nearly melted it. But Earth’s center didn’t quite melt;it______(61)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_____ (62)of the planet，”Dziewonski says idea is tame(温和的)compared to the_____(63)theories of independent geophysicist J.Marvin Herndon.Earth’s inner core is made not of iron，he claims

but a_____(64)of nickel and silicon Hemdon 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.Hemdon thinks the uranium releases heat energy as its atoms_____(65)fission-split and crash into another in a chain reaction. In other words,we may live on top of a gigantic, “natural”nuclear power plant.

51 A try B leave C turn D point

52 A create B receive C feel D overcome

53 A work B solution C job D patterns

54 A whether B what C why D how

55 A from B within C of D to

56 A followed B dominated C restored D opposed

57 A ideas B demands C phenomena D movements

58 A things B acts C methods D records

59 A taken B benefited C left D kept

60 A after B before C since D when

61 A expanded B modified C gained D melted

62 A size B origin C structure D shape

63 A radical B traditional C classical D conventional

64 A system B copy C model D compound

65 A charge B last C experience D show

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