《托福真题》.pdf

Reading Section
Directions: These sample questions in the Reading section measure your ability
to understand academic passages in English. You will read one passage and
answer questions about it. In a real test, you would have 20 minutes to read the
passage and answer the questions. Candidates with disabilities may request a
time extension.
Meteorite Impact and Dinosaur Extinction
There is increasing evidence that the impacts of meteorites have had important
effects on Earth, particularly in the field of biological evolution. Such impacts
continue to pose a natural hazard to life on Earth. Twice in the twentieth century,
large meteorite objects are known to have collided with Earth.
5 If an impact is large enough, it can disturb the environment of the entire Earth
and cause an ecological catastrophe. The best-documented such impact took
place 65 million years ago at the end of the Cretaceous period of geological
history. This break in Earth’s history is marked by a mass extinction, when as
many as half the species on the planet became extinct. While there are a dozen
10 or more mass extinctions in the geological record, the Cretaceous mass
extinction has always intrigued paleontologists because it marks the end of the
age of the dinosaurs. For tens of millions of years, those great creatures had
flourished. Then, suddenly, they disappeared.
The body that impacted Earth at the end of the Cretaceous period was a
15 meteorite with a mass of more than a trillion tons and a diameter of at least 10
kilometers. Scientists first identified this impact in 1980 from the worldwide
layer of sediment deposited from the dust cloud that enveloped the planet after
the impact. This sediment layer is enriched in the rare metal iridium and other
elements that are relatively abundant in a meteorite but very rare in the cr