共用题干 Earth's Inner CoreScientists have long struggled to understand what lies at the planet's 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 lnge Lehmann studied the waves' __________ (3) to determine that within Earth's core of molten(熔化了的)iron lies a solid inner core一but_________(4) that core was made of eluded(难倒)her. Other geophysicists quickly determined that Lehmann's inner core was composed mostly_________(5) iron.Since then,Lehmann's discovery has _________(6) conventional Earth science.But now scientists are challenging traditional theory with new and radical_________(7).For example,Earth's center could actually contain an"inner core within the inner core."claim lshii 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 Earth's center didn't 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.Dziewonski's idea is tame(温和的)compared to the_________( 13 ) theories ofindependent geophysicist J. Marvin Herndon.Earth's 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一an 8km-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正确答案C
