Earth's Inner Core
8 w- f( r6 H6 p4 a2 fScientists 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.* o4 W9 F1 H+ G7 c0 S
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.9 r3 R2 U" a# N! K, k
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.
9 Q( X. _ s/ q4 a) O* i; bAnalyzing 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.
5 t- W8 p0 N/ V3 b$ G J, G3 m& f& F% ODziewonski 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.
. @( d8 n# d9 Q- A: D3 m51 A try B leave C turn D point/ l9 `" q, I9 i& `
52 A create B receive C feel D overcome9 F7 r+ f% @. p3 Y
53 A work B solution C job D patterns
' w( x. G6 T' K. s$ U54 A whether B what C why D how2 d$ c9 h" Y: Q/ a6 {! c4 g1 r
55 A from B within C of D to4 {# _* T6 l; ^; D7 T" I% ~
56 A followed B dominated C restored D opposed
& q. [0 t& | V57 A ideas B demands C phenomena D movements
/ k; m2 r7 H7 y1 I58 A things B acts C methods D records
6 |1 ~# w3 c" _/ _, Q `( l59 A taken B benefited C left D kept
4 b* \3 N) @" Q, j60 A after B before C since D when* q+ [6 N( z6 T# R7 o( r$ [% B
61 A expanded B modified C gained D melted
" @, O I2 P8 _; j6 L' R: L( n1 y62 A size B origin C structure D shape
. ~) J4 T9 Z: k1 h63 A radical B traditional C classical D conventional2 N1 `% e! q2 h5 k3 L. u0 }5 T# A: D7 H
64 A system B copy C model D compound
' c; C, u8 T8 R: q/ }65 A charge B last C experience D show |