Official 30 Set 5

  • Q1
  • Q2
  • Q3
  • Q4
  • Q5
  • Q6

Life on Mars

  • Q1
  • Q2
  • Q3
  • Q4
  • Q5
  • Q6
What is the lecture mainly about?
  • A. Evidence proving that water was once present on Mars

  • B. Scientific analyses currently being done on mineral samples from Mars

  • C. Recent developments that could help determine whether life ever existed on Mars

  • D. An approach to determining whether amino acids on Earth originated on Mars

显示答案 正确答案: C

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    NARRATOR:Listen to part of a lecture in an astronomy class.

    MALE PROFESSOR:There's been a lot of talk recently about life on Mars, at the level of microorganisms anyway, mainly because of a few important discoveries and inventions.For example, one major discovery was that at one point water was present on Mars.How do we know?Well, in 2004, an exploration robot discovered jarosite there.

    Jarosite is a yellowish-brown mineral with a crystalline structure that's also found on Earth.It contains iron, potassium, and hydroxide.The interesting thing is that on Earth at least, it needs highly acidic water to form.So we've got water... or had it at one point.And since most planetary scientists believe that water is essential to life, the presence of jarosite means that one prerequisite for life was once present on Mars.

    But there's another thing about jarosite: one step in its formation on Earth involves microorganisms.They actually speed up the formation of jarosite dramatically.Now, theoretically it is possible for jarosite to form without the help of biological life forms-but we don't really know for sure if this happens 'cause, well, because every corner of Earth has some form of biological life.But jarosite on Earth incorporates all kinds of microorganisms into its crystalline structure.So it's possible that if the jarosite on Mars was also formed with the help of microorganisms, we might be able to detect remnants of them in the samples we find.And we have instruments now that will enable us to try to do this.For example, there's a new instrument called the microfabricated organic analyzer, or M.O.A.

    The organic analyzer is an amazing tool.It will be able to collect soil samples and analyze them right there on Mars. Pure, untouched samples.It will let us eliminate the risk we would take of contaminating the samples if they were brought back to Earth.

    And what they'll look for specifically in the soil is amino acids.

    Amino acids, as you may know, are the building blocks of proteins.In fact, there are twenty standard amino acids involved in making proteins, and lots more that aren't.And here's the important thing: amino acids are what we call handed.They can exist in two forms, which are mirror images of each other. Like hands.Right and left hands have the same number of fingers in the same order, plus one thumb.But right and left hands are not the same; they're mirror images.Well, like hands, amino acids can be right- or left-handed.And the twenty that make up the proteins on Earth are all left-handed.

    Now, one reason the M.O.A., the organic analyzer, is so impressive is that it tests not just for the presence of amino acids, but also for the handedness of amino acids.If amino acids are found, it would be especially interesting if they show a prevalence of one type of handedness, either left, like amino acids on Earth, or right.See, other physical processes in space, processes that don't involve living organisms, can create amino acids.But the ones synthesized through abiotic processes, which is to say not involving microorganisms, occur in equal numbers of right-and left-handed.[Summarizing] So, a prevalence of left-handed amino acids would indicate they were biological in origin, which would be amazing.A prevalence of right-handed ones, well that would be really amazing.Because the organisms that created them would be unlike anything we have on Earth, which produce only left-handed ones.

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    Theres been a lot of talk recently about life on Mars, at the level of microorganisms anyway, mainly because of a few important discoveries and inventions. For example, one major discovery was that at one point water was present on Mars. How do we know? Well, in 2004, an exploration robot discovered jarosite there.


    教授一开始there’s been a lot of talk 就引出关键信息 life on Mars,后面的 for example 举例里提到的水都是为了论证这一观点。

    C 选项与文意关键信息完全一致,是对全文主旨最准确的概括





Life on Mars