托福真题.doc.doc

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
10 became extinct. While there are a dozen 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.
15 The body that impacted Earth at the end of the Cretaceous period was a 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 after the impact. This sediment layer is enriched in
the rare metal iridium and other elements that are relatively abundant in a meteorite but
20 very rare in the crust of Earth. Even diluted by the terrestrial material excavated from the
crater, ponent of meteorites is easily identified. By 1990 geologists had loc