2014年6月15日托福阅读真题P1+题目+答案：Early life-forms and Earth’s Atmosphere

2014年6月15日托福阅读真题P1+题目+答案：Early life-forms and Earth’s Atmosphere 

Why has life flourished on Earth? This question has a two-part answer. First, Earth has been a cradle for life because of its position relative to the Sun. second, once life began on Earth, simple early life-forms (photosynthetic bacteria) slowly but inexorably altered the environment in a manner that not only maintained life but also paved the way for later, complex life-forms. These changes allowed later organisms to evolve and thrive. Humans and other higher organisms owe their life-supporting environment to these early life-forms.

1. The word ”altered” in the passage is closet in meaning to

A.transformed

B.protected

C.made use of

D.adapted to

2. Paragraph 1 supports which of the following inferences?

A.After complex life forms arose on Earth, bacteria quickly evolved in order to maintain favorable conditions for life.

B.Early life forms on Earth arose from the process of photosynthesis.

C.The development of complex life on Earth depended on the presence of bacteria that could be consumed by larger organisms.

D.Complex life forms on Earth may not have evolved if Earth had been farther from or closer to the Sun.

Earth’s earliest atmosphere contained several gases: hydrogen, water vapor, ammonia, nitrogen, methane, and carbon dioxide, but no oxygen. Gas mixtures emitted from present-day volcanoes resemble this early atmosphere, suggesting its origin from volcanic eruptions. In Earth’s earliest atmosphere, methane and carbon dioxide occurred at much higher levels than at present—a circumstance that was favorable for early life. Methane and carbon dioxide are greenhouse gases that warm atmospheres by retarding loss of heat to space. These two gases kept Earth warm during the Sun’s early history, when the Sun did not burn as brightly as it now does. (An early dim period, with later brightening, is normal for stars of our Sun’s type.)

3. The word ”emitted” in the passage is closet in meaning to

A.disappearing

B.examined

C.released

D.taken

4. The word ”retarding” in the passage is closet in meaning to

A.regulating

B.slowing

C.restoring

D.directing

5. In paragraph 2, why does the author provide the information that methane and carbon dioxide kept the Earth warm during the Sun’s early history?

A.To explain how the early Earth and the early Sun were related

B.To support the claim that methane and carbon dioxide are greenhouse gases

C.To explain why the high levels of methane and carbon dioxide in Earth’s early atmosphere were favorable for early life

D.To suggest that these gases affect how brightly the Sun burns

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