共用题干
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_________(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 of
independent 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.
_________(5)
A:from
B:within
C:of
D:to

相关标签： 小行星