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    #1

    Red face 2 confusing reading questions

    Since it was proposed in 1980, the Alvarezes' theory that the mass extinction of plant and animal species at the end of the Cretaceous period sixty-five million years ago resulted from a devastating extraterrestrial impact has won increasing support, although even today there is no consensus for it among scientists. In the Alvarezes' scenario, an asteroid 10 kilometers in diameter struck the earth at high velocity, forming a crater 150 kilometers wide. In addition to the immediate devastation of tidal waves, global fires, and giant storms, impact debris hurled into the atmosphere at high altitude spread around the Earth, preventing sunlight from reaching the ground. With photosynthesis blocked, herbivorous and carnivorous species died as the food chain was snapped at its base. The Alvarezes' primary evidence is a superabundance of iridium in the "Cretaceous/Tertiary boundary" (KT boundary), a thin rock stratum dividing Cretaceous rocks from those of the later Tertiary period. Iridium, relatively rare in the Earth's crust, comes mainly from the slow fall of interplanetary debris; in some KT boundary strata, iridium is 10-100 times as abundant as normal, suggesting a rapid, massive deposition. Coincident with the boundary, whole species of pollens and unicellular animals vanished from the fossil record, strongly supporting the idea of a catastrophic event. Later studies have shown that some KT boundary samples also contain osmium isotopes typical of meteorites, basalt sphericles that may have melted on impact and rapidly cooled in the atmosphere, and quartz grains deformed in a manner typical of high velocity impacts.
    Initially, paleontologists dismissed the theory, arguing that fossils of large animals such as dinosaurs showed a gradual extinction lasting millions of years. But recent intensive exploration in the Hell Creek formation of North Dakota and Montana, aimed at collecting all available dinosaur remnants rather than selectively searching for rare or well-preserved fossils, has shown an abundance of dinosaurs right up to the KT boundary. As a result, opposition to catastrophic mass extinction has substantially weakened among paleontologists.
    Given the lack of a known impact crater of the necessary age and size, and the fact that the theory requires the extinctions to have occurred in an extremely short time, some scientists have proposed alternative catastrophe scenarios. Courtillot and others have argued that massive volcanic eruptions, lasting hundreds of thousands of years, pumped enough debris into the atmosphere to cause the darkness and chemical changes that devastated life on the planet. Courtillot's evidence includes huge volcanic flows in India that coincide with the KT boundary, and analyses of KT boundary rocks that seem to show that the excess iridium was laid down over 10-100,000 years, too long for the impact hypothesis.
    Walter Alvarez and Frank Asaro reply that the shock wave caused by an impact could have melted mantle rocks, triggering the volcanic activity. They concede, though, that the exact mechanism is unclear. Meanwhile, drillings at a 150-kilometer-wide circular geologic formation in Yucatan, found in 1978 but not carefully examined until 1990, have shown a composition consistent with extraterrestrial impact. However, there is still no conclusive evidence that the Yucatan formation is the long-sought impact site.
    1. Which of the following, if true, would most weaken the theory that the Cretaceous extinctions were caused by the impact of an asteroid?
    A. The iridium layer was deposited over a period of 10,000 years.
    B. The dinosaurs flourished up until the KT boundary.
    C. The extinctions coincided with extensive volcanic activity.
    D. The location of the impact has yet to be conclusively established.
    E. The extinction of animal species accompanied the disappearance of plant life.

    The answer is D, but there is another site that gives the answer A.

    2. The author mentions "recent intensive exploration in the Hell Creek formation" primarily in order to:
    A. point out the benefits of using field research to validate scientific theories.
    B. suggest that the asteroid impact theory is not consistent with fossil evidence.
    C. discuss new fossil discoveries in North Dakota and Montana.
    D. summarize the evidence that led to wide acceptance of catastrophe scenarios of mass extinction.
    E. show that dinosaurs survived until the end of the Cretaceous period.

    The answer is E, still another site's answer is D.

    So confused! Can someone help me? Thanks a lot!!




  1. Raymott's Avatar
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    #2

    Re: 2 confusing reading questions

    Quote Originally Posted by wahaha View Post

    So confused! Can someone help me? Thanks a lot!!
    What do you think the answers should be, and why?
    Or which would you rule out?


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    #3

    Re: 2 confusing reading questions

    Doesn't A equal C in the first question? And in the last paragraph, Alvareze and Azaro offered a probable explantion against Courtillot. As for D, the site has not found yet, so no one can confirm the Alvareze's theory. Thus, I think D is the proper answer.

    In the second quesion, both D and E are correct answers. But given the word "primarily", I would choose D as the coorect answer.

  2. Raymott's Avatar
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    #4

    Re: 2 confusing reading questions

    Quote Originally Posted by wahaha View Post
    Doesn't A equal C in the first question?
    Certainly not on a superficial inspection. A is about iridium deposition (which "
    comes mainly from the slow fall of interplanetary debris"), and C is about volcanic activity (which doesn't).

    And in the last paragraph, Alvareze and Azaro offered a probable explantion against Courtillot. As for D, the site has not found yet, so no one can confirm the Alvareze's theory. Thus, I think D is the proper answer.
    I disagree.
    "D.
    The location of the impact has yet to be conclusively established."
    This is neither here nor there.


    In the second quesion, both D and E are correct answers. But given the word "primarily", I would choose D as the coorect answer.
    So would I.

    Here are my answers - 1A, 2D

    1.
    Which of the following, if true, would most weaken the theory
    D doesn't weaken the theory because it's quite irrelevant It's illogical to say "The asteroid theory is wrong because we aren't exactly sure yet where it hit.
    E. is obviously wrong because it supports the theory
    C. This may be true, but there has often been a lot of extensive volcanic activity. This doesn't really count as evidence against a competing theory.
    B. is wrong because, like E, it supports the theory.
    A is right, because the proponents of the theory associated a sudden, massive extinction with an acute, massive rise in extra-terrestrial iridium levels. If it can be shown that these iridium levels where in fact laid down over 10,000 years, it's unlikely they were deposited by an asteroid. Also, this is the "
    Alvarezes' primary evidence". Surely if you throw doubt on the proponent's primary evidence, that is the factor that, if true, would most likely to weaken their case?


    2. The author mentions "recent intensive exploration in the Hell Creek formation" primarily in order to:
    A. is wrong. This is a specific article about the Alvarezes' theory.
    B. is obviously wrong because it actually supports the asteroid theory.
    C. is wrong because the article is not about fossil finds in
    North Dakota and Montana.
    E. is wrong. Whether
    dinosaurs survived until the end of the Cretaceous period is not at issue. The point is whether they all died at the KT point.
    This leaves D. which I would call the right answer, but it's not a well-asked question. Certainly the text asserts that the "a
    s a result [of the "Hell Creek formation] opposition to catastrophic mass extinction has substantially weakened among paleontologists." This is absolutely essential to the asteroid theory; that's why it was mentioned.
    However, it's wrong to claim that this one aspect "
    summarizes the evidence that led to wide acceptance of catastrophe scenarios of mass extinction". It merely gives the most compelling evidence. But I think that's what is meant.


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    #5

    Lightbulb Re: 2 confusing reading questions

    Thank you, Raymott.

    The first question concerns about the first paragraph, which I totally missed. Thanks for your patience to read and answer my questions.
    You really clear up my confusion!

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