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Official GMAT Prep RC Main Idea Passage

This topic has 3 expert replies and 2 member replies
richachampion Legendary Member
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Official GMAT Prep RC Main Idea Passage

Post Thu Jul 13, 2017 8:54 pm
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    Prior to 1965 geologists assumed that the two giant rock plates meeting at the San Andreas Fault generate heat through friction as they grind past each other, but in 1965 Henyey found that temperatures in drill holes near the fault were not as elevated as had been expected. Some geologists wondered whether the absence of friction-generated heat could be explained by the kinds of rock composing the fault. Geologists’ pre-1965 assumptions concerning heat generated in the fault were based on calculations about common varieties of rocks, such as limestone and granite; but “weaker” materials, such as clays, had already been identified in samples retrieved from the fault zone. Under normal conditions, rocks composed of clay produce far less friction than do other rock types.

    In 1992 Byerlee tested whether these materials would produce friction 10 to 15 kilometers below the Earth’s surface. Byerlee found that when clay samples were subjected to the thousands of atmospheres of pressure they would encounter deep inside the Earth, they produced as much friction as was produced by other rock types. The harder rocks push against each other, the hotter they become; in other words, pressure itself, not only the rocks’ properties, affects frictional heating. Geologists therefore wondered whether the friction between the plates was being reduced by pockets of pressurized water within the fault that push the plates away from each other


    The passage is primarily concerned with

    A. evaluating a method used to test a particular scientific hypothesis
    B. discussing explanations for an unexpected scientific finding
    C. examining the assumptions underlying a particular experiment
    D. questioning the validity of a scientific finding
    E. presenting evidence to support a recent scientific hypothesis

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    richachampion Legendary Member
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    Post Thu Jul 13, 2017 8:55 pm
    I want experts to please chime in to help me to eliminate the answer choices.

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    Post Sun Jul 16, 2017 2:55 am
    richachampion wrote:
    Prior to 1965 geologists assumed that the two giant rock plates meeting at the San Andreas Fault generate heat through friction as they grind past each other, but in 1965 Henyey found that temperatures in drill holes near the fault were not as elevated as had been expected. Some geologists wondered whether the absence of friction-generated heat could be explained by the kinds of rock composing the fault. Geologists’ pre-1965 assumptions concerning heat generated in the fault were based on calculations about common varieties of rocks, such as limestone and granite; but “weaker” materials, such as clays, had already been identified in samples retrieved from the fault zone. Under normal conditions, rocks composed of clay produce far less friction than do other rock types.

    In 1992 Byerlee tested whether these materials would produce friction 10 to 15 kilometers below the Earth’s surface. Byerlee found that when clay samples were subjected to the thousands of atmospheres of pressure they would encounter deep inside the Earth, they produced as much friction as was produced by other rock types. The harder rocks push against each other, the hotter they become; in other words, pressure itself, not only the rocks’ properties, affects frictional heating. Geologists therefore wondered whether the friction between the plates was being reduced by pockets of pressurized water within the fault that push the plates away from each other


    The passage is primarily concerned with

    A. evaluating a method used to test a particular scientific hypothesis
    B. discussing explanations for an unexpected scientific finding
    C. examining the assumptions underlying a particular experiment
    D. questioning the validity of a scientific finding
    E. presenting evidence to support a recent scientific hypothesis
    Temperatures in drill holes near the fault were not as elevated as had been expected.
    Some geologists wondered whether...
    Byerlee tested whether...
    Geologists therefore wondered whether...


    The passage is primarily concerned with
    B: discussing explanations for an unexpected scientific finding.
    The red portion in the passage matches the red portion in the answer choice above.
    The blue portions in the passage match the blue portion in the answer choice above.

    The correct answer is B.

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    Post Sun Jul 16, 2017 4:55 am
    richachampion wrote:
    Prior to 1965 geologists assumed that the two giant rock plates meeting at the San Andreas Fault generate heat through friction as they grind past each other, but in 1965 Henyey found that temperatures in drill holes near the fault were not as elevated as had been expected. Some geologists wondered whether the absence of friction-generated heat could be explained by the kinds of rock composing the fault. Geologists’ pre-1965 assumptions concerning heat generated in the fault were based on calculations about common varieties of rocks, such as limestone and granite; but “weaker” materials, such as clays, had already been identified in samples retrieved from the fault zone. Under normal conditions, rocks composed of clay produce far less friction than do other rock types.

    In 1992 Byerlee tested whether these materials would produce friction 10 to 15 kilometers below the Earth’s surface. Byerlee found that when clay samples were subjected to the thousands of atmospheres of pressure they would encounter deep inside the Earth, they produced as much friction as was produced by other rock types. The harder rocks push against each other, the hotter they become; in other words, pressure itself, not only the rocks’ properties, affects frictional heating. Geologists therefore wondered whether the friction between the plates was being reduced by pockets of pressurized water within the fault that push the plates away from each other


    The passage is primarily concerned with

    A. evaluating a method used to test a particular scientific hypothesis
    B. discussing explanations for an unexpected scientific finding
    C. examining the assumptions underlying a particular experiment
    D. questioning the validity of a scientific finding
    E. presenting evidence to support a recent scientific hypothesis
    We get the gist of where this passage is going in the first sentence: Prior to 1965 geologists assumed that the two giant rock plates meeting at the San Andreas Fault generate heat through friction as they grind past each other, but in 1965 Henyey found that temperatures in drill holes near the fault were not as elevated as had been expected

    So we have this unexpected finding that contradicts prior expectations. (The "but" is a dead-giveaway here.) The remainder of the passage grapples with why such an anomalous finding may have resulted. Because clay tends to be cooler? Because of pockets of pressurized water?) The answer is B

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    Post Sun Jul 16, 2017 12:34 pm
    I got a private request to respond to this one. Since I saw that 2 other experts had responded already, though, I took a different approach: I tried to see if I could guess the answer without reading the passage! Here's my analysis of the language alone:

    A. evaluating a method used to test a particular scientific hypothesis
    When we're conducting scientific tests, we're usually concerned with 2 things: 1) the findings/data, and 2) what conclusions can be drawn from them. The methods used to gather data or test hypotheses are usually secondary. Even if a passage said effectively "this was a useful method," it would be because it allowed us to draw certain inferences. That would be the main idea instead.

    B. discussing explanations for an unexpected scientific finding
    This sounds plausible - passages very often discuss explanations for findings. The word "unexpected" skews a bit negative, so that's giving me pause. The passage would have to be like "We found this surprising thing. Here are a few things that might explain it."

    C. examining the assumptions underlying a particular experiment
    Assumptions underlying a hypothesis, sure. But underlying the experiment itself? I'm not sure what that would even mean. They're testing the wrong thing, or using a bad method to test it? Perhaps, but as with A, the methods of testing are almost always less important than the conclusions drawn.

    D. questioning the validity of a scientific finding
    Passages will often present evidence that questions a theory or a conclusion. It's more rare to question a finding. We can usually assume that findings are objectively true. This seems unlikely.

    E. presenting evidence to support a recent scientific hypothesis
    This seems perfectly plausible. Lots of science passages are structured to do exactly this.

    So without reading the passage, I'd say that E and B seem the most plausible / have the fewest red flags. And when I scroll down... it turns out that B was correct.

    This kind of analysis won't always work, of course. I'm not recommending that you skip reading the passage altogether! But it's a really good exercise: are you focused on the specific language of the answer choices, rather than just thinking about the general content?

    More on how to think about the provability of answer choices here: https://www.manhattanprep.com/gmat/blog/2017/03/28/how-to-hack-gmat-reading-comprehension-think-like-a-lawyer/
    (I have no idea why there's a picture of a frog!)

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    richachampion Legendary Member
    Joined
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    Posted:
    678 messages
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    24 members
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    31 times
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    GMAT Score:
    740
    Post Tue Jul 25, 2017 10:01 pm
    Dear Experts
    GMATGuruNY
    DavidG@VeritasPrep and
    ceilidh.erickson


    I have posted one more question here RC Mian Idea Question.

    Please help me with your analysis on this question also.

    _________________
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