练习步骤说明（黄色小点标记的是当天任务）
并在Step4之后增加单句听译的练习步骤。
25分以上的同学Stpe5可以省略，做完题直接对照笔记示范改进一下笔记即可。
全文音频
题目
1 What is the Iecture mainly about?
A How researchers determine the rate at which Earth cooled
B How climate change affected early life on Earth
C Evidence that challenges a belief about the early conditions on Earth
D Conflicting scientific hypotheses about the age of Earth
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2 Prior to the 1980s researchers believed that Earth’s climate was extremely hot during its first 500 million years. What led researchers to this belief?
A No undamaged rocks from that period had been found.
B Organisms from that period indicate that they survived extreme conditions
C Every mountain from that period had experienced intense volcanic activity.
D Zircon crystals from that period contain evidence of hot conditions
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3 According to the professor, what is true about the mineral zircon?
Pick all correct answers.
A It is very durable.
B It can form around other substances.
C Most of it was destroyed during Earth’s first 500 million years.
D It requires extremely high temperatures to form
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4 The professor mentions research done in Australia in the 1980s. What is the professor’s opinion of the result of that research?
A It was disappointing, because a new technology provided unreliable data
B It was unexpected, because it disproved the most accepted theory
C It was misleading, because it reinforced an incorrect theory
D It was useful, because it led researchers to question a theory
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5 Why does the professor say this:
A To express his surprise at an error made by researchers
B To stress the significance of the facts he is relating
C To remind the students about something he already taught
D To acknowledge that his opinion differs from that of most researchers
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6 What can be concluded from the information obtained from the improved ion microprobe?
A Earth‘s climate began to cool down earlier than previously believed.
B Life appeared on Earth later than previously believed.
C Some water present on early Earth was frozen.
D Zircon was the most common mineral present on early Earth.
