托福阅读真题+题目+答案：Ocean and Atmosphere on Early Earth

托福阅读真题+题目+答案：Ocean and Atmosphere on Early Earth

Where did Earth's ocean water come from? Scientists agree that a large amount of water must have arrived during planet, accretion, which is the process of collision and sticking together of the material in orbit around the Sun by which Earth and the other planets in the solar system formed 4.6 billion years ago. Perhaps significant volumes were added during the period of heavy bombardment, during which Earth was being hit by a large number of comets (whose nuclei are composed mostly of ice) and other objects left over from the formation of the planets. The volume of water eventually found on Earth may be related to the formation of Earth's core (innermost layer). When the iron- and nickel-rich core formed, most of the water in the forming planet was consumed in oxidation processes whereby the oxygen component of water was used to make iron and nickel oxides. It is the residual water that make up the oceans. Perhaps that residual quantity was significantly enhanced by water carried by comets after Earth's initial formation, perhaps not .1n either case, the oceans reached approximately their present volume by 3.8 billion years ago. But this does not mean they were at their present area. Geologist Don Lowe has estimated that before 3 billion years ago, less than 5 percent of Earth's surface was land. Earth's atmosphere was also very different from that of today. There was no oxygen, and there was a great d.1 more carbon dioxide (Co2)—perhaps 100 to 1,000 times as much as today.

1.Which of the sentences below best expresses the essential information In the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

O Earth formed through a process of collision and sticking together of material in orbit around the Sun.

O Scientists agree that Earth and the other planets formed tough planetary accretion 4.6 billion years ago.

O A large amount of water must have arrived on Earth as it formed through accretion 4.6 billion years ago.

O Earth and the other planets in the solar system must have received a large amount of water through planetary accretion.

2.The word “estimated”In the passage is closest in meaning to

O proposed

O strongly argued

O roughly calculated

O indicated

3.According to paragraph 1, which of the following is true of Earth's early oceans?

O They were first formed by water that was brought to Earth by comets after the planet was formed.

O They contained about the same amount of water 3.8 billion years ago as they do today.

O They covered less than 5 percent of Earth's surface until about3 billion years ago.

O They did not have enough volume to cover their present surface area.

Earth's surface temperature was higher than it is now because more heat was emanating from the interior and because of the warming generated by the extensive CO2 and other greenhouse gases in the atmosphere. Greenhouse gases trap heat near the surface through the so-called greenhouse effect. Earth's internal generation of heat was an important factor; the Sun at this time was much fainter, a delivering perhaps a third less energy, than at the present time.

4. Why does the author state that "the Sun at this time was much fainter, a delivering perhaps a third less energy, than at the present time”?

O To suggest that early Earth's surface temperature should have been significantly cooler than it is now

O To support the claim that early Earth's atmosphere was very different from that of today

O To cast doubt on the role of carbon dioxide and other greenhouse gases in early Earth's high surface temperature

O To explain why the heat coming from Earth's interior was important for early Earth's surface temperature

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