托福阅读常考话题及练习题推荐五：恐龙大灭绝（3）

1托福阅读常考话题：恐龙大灭绝练习题

Paragraph 4: Explanations for the K-T extinction were revolutionized in 1980 when a group of physical scientists led by Luis Alvarez proposed that 65 million years ago Earth was stuck by a 10-kilometer-wide meteorite traveling at 90,000 kilometers per hour. They believed that this impact generated a thick cloud of dust that enveloped Earth, shutting out much of the incoming solar radiation and reducing plant photosynthesis to very low levels. Short-term effects might have included huge tidal waves and extensive fires. In other words, a series of events arising from a single cataclysmic event caused the massive extinctions.Initially, the meteorite theory was based on a single line of evidence.At locations around the globe, geologists had found an unusually high concentration of iridium in the layer of sedimentary rocks that was formed about 65 million years ago.Iridium is an element that is usually uncommon near Earth’s surface, but it is abundant in some meteorites.Therefore, Alvarez and his colleagues concluded that it was likely that the iridium in sedimentary rocks deposited at the K-T boundary had originated in a giant meteorite or asteroid. Most scientist came to accept the meteorite theory after evidence came to light that a circular formation, 180 kilometers in diameter in diameter and centered on the north coast of the Yucatan Peninsula, was created by a meteorite impact about 65 million years ago.

7. The word “generated” in the passage is closest in meaning to

A. collected

B. produced

C. spread

D. added

8. The word “extensive” in the passage is closest in meaning to

A. widespread

B. sudden

C. numerous

D. subsequent

9. According to paragraph 4, all of the following contributed to the massive extinctions of the K-T period EXCEPT:

A. tidal waves

B. fires

C. insufficient solar radiation

D. iridium

10. According to paragraph 4, which of the following statements explains the importance of the discovery of high levels of iridium rocks?

A. It provided evidence that overexposure to solar radiation led to the K-T extinction.

B. It showed that more than one cataclysmic event was responsible for the K-T extinction.

C. It suggested that the cause of the K-T extinction may have been a meteorite striking Earth.

D. It provided evidence that the K-T extinction occurred 65 million years ago.

11. According to paragraph 4, which of the following is true about the Yucatan Peninsula?

A. The circular formation there was caused by a meteorite impact 65 million years ago.

B. Sedimentary rocks from that area have the lowest iridium concentration of any rocks on Earth.

C. There is evidence that a huge tidal wave occurred there 65 million years ago.

D. Evidence found there challenged the meteorite impact theory.

12. Which of the following can be inferred from paragraph 4 about the meteorite theory?

A. The data originally presented as evidence for the theory were eventually rejected.

B. Many scientists did not accept it when it was first proposed.

C. It has not been widely accepted as an explanation for the K-T extinction.

D. Alvarez subsequently revised it after a circular formation was found in the Yucatan Peninsula.

Paragraph 4: Explanations for the K-T extinction were revolutionized in 1980 when a group of physical scientists led by Luis Alvarez proposed that 65 million years ago Earth was stuck by a 10-kilometer-wide meteorite traveling at 90,000 kilometers per hour. They believed that this impact generated a thick cloud of dust that enveloped Earth, shutting out much of the incoming solar radiation and reducing plant photosynthesis to very low levels. Short-term effects might have included huge tidal waves and extensive fires. In other words, a series of events arising from a single cataclysmic event caused the massive extinctions. ■ Initially, the meteorite theory was based on a single line of evidence. ■ At locations around the globe, geologists had found an unusually high concentration of iridium in the layer of sedimentary rocks that was formed about 65 million years ago.■ Iridium is an element that is usually uncommon near Earth’s surface, but it is abundant in some meteorites. ■ Therefore, Alvarez and his colleagues concluded that it was likely that the iridium in sedimentary rocks deposited at the K-T boundary had originated in a giant meteorite or asteroid. Most scientist came to accept the meteorite theory after evidence came to light that a circular formation, 180 kilometers in diameter in diameter and centered on the north coast of the Yucatan Peninsula, was created by a meteorite impact about 65 million years ago.

13. Look at the four squares [■] that indicate where the following sentence can be added to the passage.

This focused on the chemical composition of ancient rocks.

Where would the sentence best fit?

Click on a square [■] to insert the sentence in the passage

14. 【Directions】 An introductory sentence for a brief summary of the passage of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some answer choices do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This questions is worth 2 points.

The K-t extinction 65 million years ago is the best known of the five major extinction episodes since the Cambrian period.

Answer Choices

A. Collectively, the five major extinction episodes resulted in the elimination of a larger number of species than did all the minor extinction events.

B. The K-T extinction eliminated the dinosaurs and ammonoid mollusks but was followed by the diversification of mammals and gymnospermous plants.

C. An extreme cooling of the climate could not have caused the K-T extinction of dinosaurs, because, while most dinosaurs depended on environmental heat, some did not.

D. The K-T extinction of the dinosaurs is the only mass extinction that has been explained by the impact of a meteorite.

E. In1980 Luis Alvarez proposed that the K-T extinction was caused by ecological disasters brought about by the impact of a meteorite striking Earth.

F. A high concentration of iridium in sedimentary rocks at the K-T boundary and a large impact crater in the Yucatan Peninsula from 65 million years ago strongly support Alvarez’ hypothesis.