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1996 年 10 月托福阅读全真试题
Question 1-8
When Jules Verne wrote Journey to the Center of the Earth in 1864 , there were
many conflicting theories about the nature of the Earths interior. Some geologists
thought that it contained a highly compressed ball of incandescent gas , while others
suspected that it consisted of separate shells , each made of a different material.
Today, well over a century later , there is still little direct evidence of what
lies beneath our feet. Most of our knowledge of the Earths interior comes not from
mines or boreholes , but from the study of seismic waves - powerful pulses of energy
released by earthquakes.
The way that seismic waves travel shows that the Earths interior is far from
uniform. The continents and the seabed are formed by the crust - a thin sphere of
relatively light , solid rock. Beneath the crust lies the mantle , a very different
layer that extends approximately halfway to the Earths center. There the rock is the subject of a battle between increasing heat and growing pressure.
In its high levels , the mantle is relatively cool ; At greater depths , high
temperatures make the rock behave more like a liquid than a solid. Deeper still ,
the pressure is even more intense , preventing the rock from melting in spite of a higher temperature.
Beyond a depth of around 2, 900 kilometers , a great change takes place and the
mantle gives way to the core. Some seismic waves cannot pass through the core and
others are bent by it. From this and other evidence , geologists conclude that the
outer core is probably liquid , with a solid center. It is almost certainly made of
iron , mixed with smaller amounts of other elements such as nickel.
The conditions in the Earths core make it a far more alien world than space.
Its solid iron heart is subjected to unimaginable pressure and has a temperature of
about 9, 000oF. Although scientists can speculate about its nature , neither humans
nor machines will ever be able to visi
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