The Grand Canyon, a long, narrow gorge in Arizona, is rich in geological history. It record of past plant and animal life also makes it an exciting and invaluable object of study for biologists. Using samples from the two hundred and seventeen miles of the canyon's walls, scientists analyze the building materials that form the earth's surface and study the natural process which have affected the canyon over its four billion-year history. These processes include the eruption of volcanoes, which were active as recently as one thousand years ago, and gradual decomposition by erosion. Scientist also study a great variety of fossils that can be found in the canyon. These imprints of past forms of life are preserved in rock. The lower levels of canyon rock contain fossils of sea-shells and primitive algae, while the upper levels contain fossils of such creatures as dinosaurs and other prehistoric land animals. All of these discoveries provide scientist with information both on the earth's history in general and on the area around the Grand Canyon in particular.
What is the main topic of this passage ?
- The fascination of geological history
- The effect of volcanoes on the Grnad Canyon
- Prehistoric plants and animals
- A record of natural history of the Grand Canyon
According to the passage, why is the Grand Canyon of special importance to the geologist ?
- It reveals much of the earth's past.
- It is longer and deeper than any other canyon.
- It has suffered little destriction over the years.
- It is completely dry all year long.
Scientists can learn about previous life in the area by studying .
- current animal life
- impressions in rocks
- feeding habits of dinosaurs
- construction materials
Which of the following statements about the Grand Canyon can be concluded from the passage ?
- It is much older than other parts of the United States
- It contains more levels than other canyons.
- Its history is more varied and accessible than that of other areas.
- Its former habitation by dinosaurs was an unexpected discovery.
아리조나에 있는 길고 좁은 계곡인 Grand canyon은 지질학상 가치 있는 곳이다. 이 지역은 과거의 동식물 생태에 관한 풍부한 기록 때문에 생물학자들에게 흥미롭고 매우 귀중한 연구대상이다. 과학자들은 217마일에 이르는 Canyon의 암벽 표본을 이용하여 땅의 표면을 형성하고 있는 구성물질을 분석하고, 거의 40억년간 Canyon에 영향을 끼쳐온 자연계의 작용을 연구하고 있다. 이러한 작용들 가운데 최근 천년까지 활동했던 화산의 폭발과 침식작용에 의한 점차적인 분해작용이 포함되어 있다. 과학자들은 Canyon에서 발견되는 아주 다양한 화서들을 연구한다. 이러한 과거 생물의 형태의 흔적이 바위 속에 보존되어 있다. Canyon의 암벽 하층부에는 바닷조개와 원시 해초의 화석이 포함되어 있다. 이런 모든 발견들은 과학자들에게 광범위하게는 지구의 역사에 대한 정보를 제공하고 세부적으로 Grand Canyon의 주변 지방들에 대한 정보를 제공한다.