PrepTest 151

[lcid:3700] Prep Test 151 LSAT — Reading Comp — S1 Reading comp

Passage

Questions 22-27  .       According to the generally accepted theory of  . plate tectonics, the earth's crust consists of a dozen Remaining source text redacted.
Passage walkthrough
Passage Summary

Topic: Science


Paragraph 1

  • Paragraph note
    • Background info on "plate tectonics" and central question (why some areas have lots of subduction but no earthquakes)
  • Views, minor Meta-Structures, and the author's attitude
    • Definitions:
      • Plate tectonics: The earth's crust features many plates of solid rock that move across the mantle (first sentence)
      • Mantle: The slightly fluid layer of rock between crust and core (first sentence)
      • Subduction: The process in which two plates collide and one plate is forced under the other until it merges with the mantle (third and fourth sentences)
      • Earth's seismic "hot zones": Regions with very high levels of subduction (fifth sentence)
    • Cause-and-effect relationship, according to the theory of plate tectonics:
      • Earthquakes are caused by two plates grinding against each other as they collide, which causes subduction, which causes an enormous build-up of energy abruptly released as an earthquake (second and fifth sentences)
    • Author attitude: "generally accepted" (first sentence); "contrary to expectations" (sixth sentence); "crucial question" (last sentence); "no answer" (last sentence)

Paragraph 2

  • Paragraph note
    • Answer: Earthquakes are caused by subduction from plates moving in the opposite direction, not the same direction
  • Views, minor Meta-Structures, and the author's attitude
    • Comparisons of two subduction types:
      • When plates move toward each other, the resulting subduction is relatively motionless and shallow, the amount of friction is higher, and the likelihood of earthquakes is increased (second, third, seventh, and last sentences)
        • This amount of resistance is compared to two pieces of sandpaper rubbing against each other (last sentence)
      • On the other hand, when plates move in the same direction, the resulting subduction is high velocity and steep, the amount of friction between places is lower, and there is a lower likelihood of earthquakes (fourth, fifth, and sixth sentences)
        • This type of deduction is compared to an oar being dipped in water from a moving boat (fifth sentence)

Paragraph 3

  • Paragraph note
    • Implications: Areas with "low" subduction may be at a greater risk of earthquakes than previously thought
  • Views, minor Meta-Structures, and the author's attitude
    • Author's attitude: "provides a warning" (first sentence); "may in fact be at a significant risk of earthquakes" (last sentence)

Main Point: Some scientists believe that the type of subduction caused by two plates moving in the same direction can explain why some regions feature intense subduction and relatively few earthquakes.

Key Lines?

Paragraph 1, Sentence 7 (P1, S7) - Question

P2, S8-9 - Answer

P3, S1 - Implications

Meta-Structure?

Question/Answer: We think the Question/Answer Meta-Structure is the closest fit for this passage*. In such a passage, the author will usually pose a question and consider one or more answers for the rest of the passage. And that's the approach that this author uses. After providing some background information on plate tectonics and seismic "hot zones," the author asks a question: "[H]ow can often intense subduction take place at certain locations with little or no seismic activity?" (P1, S7). The author uses the remaining two paragraphs to discuss the answer to this question.

In such a passage, the main point is typically the answer. Here, the author seems to buy the explanation offered by a group of scientists who believe earthquakes are more likely to occur when plates collide when sliding toward each other rather than sliding in the same direction. So, we've summarized that answer as, "Some scientists believe that the type of subduction caused by two plates moving in the same direction can explain why some regions feature intense subduction and relatively few earthquakes."

*Truthfully, about half of the Meta-Structures could describe this passage. Certainly, you could call this a Phenomenon/Explanation, Proposing a Hypothesis, Correcting the Record, Reporting a Viewpoint, or Old Approach/New Approach passage. One could even make a reasonable case that this is a Paradox/Resolution or Problem/Solution passage. Any one of these Meta-Structures could help us understand the passage's structure and main point. Ultimately we went with Question/Answer because the passage explicitly proposes a question and discusses the answer. But if you went with one of the other Meta-Structures, that's OK. Remember, the Meta-Structures are tools that help us think about the overarching structure and ideas in a passage. We don't have to agree on which Meta-Structure a passage has to realize the benefits of the Meta-Structures, as this passage illustrates.

Comparisons: This passage — especially the second paragraph — utilizes the comparison minor Meta-Structure extensively. Most of the comparisons deal with the difference between the two types of subduction zones. We will almost certainly get a few questions that relate to these differences, so let's review the details of each.

  • Head-on subduction:
    • More likely to lead to earthquakes.
    • Subduction is relatively motionless.
    • Subduction occurs at a shallower angle of descent.
    • There is a larger plane of contact with the plates and thus more friction and seismic activity.
  • Same-direction subduction
    • Less likely to lead to earthquakes.
    • Subduction occurs at a high velocity.
    • Subduction occurs at a steeper angle of descent.
    • There is less contact between the plats and thus less friction and seismic activity.

Last Thoughts?

Let's make sure we understand these two types of subduction for the inevitable Minor Point questions about them. A stumbling block for many test-takers is that the fast-moving, steep-descending plates that experience significant resistance from the mantle are less likely to cause earthquakes. Expect the test-writers to try to trick us by playing up that counterintuitive fact.

Question prompt

Which one of the Remaining source text redacted.
Why the credited answer is right

Credited answer: E

The notes below walk through why it fits the stem and how to eliminate the rest.

Question Type

Science

Strategy Overview

Remind ourselves of the main point of the passage, then head to the answers, focusing on those that line up with the main point and then using our notes/the passage to find the correct answer

Answer Anticipation

This is yet another question that asks us to infer an answer choice that must be true. However, this question's topic — seismic activity — is so broad that it covers the entire passage.So, rather than review the passage for references to "seismic activity," we should rely on our big-picture understanding of the passage to answer this question. We should start by reminding ourselves of the main point (either by reviewing what we said after reading the passage or by rereading our answer to the main point question). From there, we can head to the answer choices. If something in an answer choice doesn't seem familiar, we shouldn't check the passage to see if it was mentioned. Instead, we'll table it and move on to the next answer choice. If something seems inconsistent with the main point, we can eliminate it. If something seems familiar and consistent with the main point, we'll use our notes/highlights/underlines to find the part of the passage that proves the answer choice must be true. If we can find that confirmation, we'll select that answer choice and move on.

Answer choices

  1. A
    Earthquakes are frequent in Remaining source text redacted.
    Why choice A is not credited

    (A) Do you recall reading that earthquakes are common in any zone with "considerable motion of colliding plates"?

    Many test-takers choose this one — likely because they overlooked the main point when answering this question (or misunderstood the main point when reading the passage). If we recall the question and answer this passage is organized around, we'd realize that (A) contradicts the passage's main point. The main point held that regions can have "considerable motion of colliding plates" with very few earthquakes when the plates are moving in the same direction (P2, S7). So it's not true that earthquakes will be common in any zone with considerable collision. Therefore, we can eliminate (A).

  2. B
    Earthquakes are equally likely Remaining source text redacted.
    Why choice B is not credited

    (B) Do you recall reading that earthquakes are equally likely to occur at any point along the plane of contact between two colliding plates?

    Probably not. Expert test-takers would also be scared away by the strong, hard-to-support language in this answer choice ("equally likely," "any point") and may opt to eliminate this one on sight. At any rate, if you don't remember reading this detail, you shouldn't waste time reviewing the passage to see if it is supported. Just table it and move on to the next one.

    If we had to review the passage, we wouldn't find any support for (B). Although we are told that the size of the plane of contact matters, we do not know where an earthquake may or may not occur on that plane. So this fact cannot be inferred.

  3. C
    Seismic quiet zones are Remaining source text redacted.
    Why choice C is not credited

    (C) Do you remember reading that "quiet zones" are at risk of the "very gradual accumulation of energy" that is infrequently released?

    Probably not. However, many test-takers select this answer choice, perhaps because they misunderstand the last paragraph. It's tempting to conclude the last paragraph implies that seismically quiet zones are risky because of the gradual accumulation of energy. However, such an interpretation ignores the passage's main point. The last paragraph warns us that regions with low levels of subduction may be risky because these regions could feature the shallow-angle subduction that results from plates moving toward each other. The last paragraph doesn't warn us about seismically quiet zones in general — just those with low levels of subduction. And the passage never says anything about the gradual build-up of energy. So, we can eliminate this one.

  4. D
    No region can be Remaining source text redacted.
    Why choice D is not credited

    (D) Do you recall reading that we can't identify any region as a subduction zone unless an earthquake occurred there?

    Probably not! In fact, the central mystery this passage addresses is why some areas have high levels of subduction but no earthquakes (P1, S7). So, we must be able to identify some areas as subduction zones despite the lack of earthquakes.

  5. E
    Earthquakes are more likely Remaining source text redacted.
    Why choice E matches the stem

    (E) Do you recall reading that earthquakes are more likely to result where there is a large plane of contact between the plates during subduction?

    Probably! This is consistent with the main point that shallow-angle subduction (which would create a larger plane of contact between the plates than steep-angle subduction) is more likely to lead to earthquakes. And if we needed to review the passage to confirm this claim's veracity, we'd find that this matches the language of the last two sentences of the second paragraph. Those sentences claim that a large plane of contact between plates is like sandpaper, which leads to a lot of friction and more earthquakes (P2, S8-9). Therefore, we can be confident that this is correct.

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