PrepTest 133

[lcid:3631] Prep Test 133 LSAT — Reading Comp — S4 Reading comp

Passage

Questions 16-21  .        Until the 1950s, most scientists believed that the  . geology of the ocean floor had remained Remaining source text redacted.
Passage walkthrough
Passage Summary

Topic: Science


Paragraph 1

  • Paragraph note
    • Old belief (ocean floor unchanged) and the first in a list of discoveries that made old belief unsupportable (variations in basalt's polarity)
  • Views, minor Meta-Structures, and the author's attitude
    • Old belief:
      • The geology of ocean floor has been unchanged for millions of years (first sentence)
    • New belief (post-1950):
      • Based on new discoveries, it's clear that the ocean floor's geology has changed (second sentence)
    • List of new discoveries:
      • Odd magnetic variations in the basalt on the ocean floor; some align with Earth's magnetic field; others reversed (third through sixth sentences)
    • Definition of magnetite: strongly magnetic mineral (fourth sentence)
    • Definition of "normal" polarity: polarity that is aligned with Earth's current magnetic field (fifth sentence)
    • Definition of "reversed" polarity: polarity that is the opposite of Earth's current magnetic field (fifth sentence)
    • Cause-and-effect relationship, according to the author:
      • Earth's current magnetic field causes magnetite to possess a normal or reversed polarity, which is "locked in" as magnetite cools to form basalt (sixth through last sentences)
    • Author's attitude: "insupportable" (second sentence); "not entirely surprising" (fourth sentence)

Paragraph 2

  • Paragraph note
    • The second in a list of discoveries that made old belief unsupportable (stripes of rock with different polarities along mid-ocean ridge, ocean floor spreading)
  • Views, minor Meta-Structures, and the author's attitude
    • Definition of "mid-ocean ridge": Underwater mountain range that winds around the Earth (first sentence)
    • Scientists' view:
      • The mid-ocean ridge is a structurally weak zone where the ocean floor gets pulled apart, and new rock forms from magma that emerges in this zone; this process is called ocean floor spreading (third through last sentences)
    • Author's attitude: "great oceanic discovery" (first sentence)

Paragraph 3

  • Paragraph note
    • Evidence that supports ocean floor spreading theory (stripes of rocks match the polarity of Earth's magnetic reversals)
  • Views, minor Meta-Structures, and the author's attitude
    • List of evidence that supports ocean floor spreading theory, according to the author:
      • The rocks are young at peak and older as you move away (second sentence)
      • The oungest rocks all have normal polarity (third sentence)
      • If we assume the ocean spreads 1 cm/year, the striping pattern matches when Earth's magnetic reversals occurred (last sentence)
    • Author's attitude: "was supported" (first sentence); "remarkable correlation" (last sentence)

Main Point: Following new discoveries on the ocean floor, scientists in the 1950s adopted the new belief that the geology of the ocean floor has been changing over the past millions of years.

Meta-Structure?

Correcting the Record: This passage best fits the Correcting the Record Meta-Structure.* In such a passage, the author typically begins by describing a common misconception or false belief. Often, this false belief is based on a lack of information. Then, the author explains why this past belief is false or misleading, occasionally offering an alternative belief. In this passage, we learn that scientists used to the false belief that the ocean floor didn't change over millions of years. The author corrects this belief in light of recent evidence. The new belief holds that the ocean floor has changed considerably, especially through the ocean floor spreading along the mid-ocean ridge.

In a passage that uses a Correcting the Record Meta-Structure, the main point is often the author’s explanation of why the misconception is false. However, if the author provides an alternative belief, the main point will be the author’s opinion about that belief. Since the author provides the new belief on ocean floor spreading, we made the crux of our anticipated main point.

*As is often the case with passages that use a Critical Meta-Structure, several other Meta-Structures from this family could also describe this passage. Certainly, we could call this an Old Approach/New Approach passage (or perhaps more precisely, an Old Theory/New Theory passage). The passage brings up an old approach and the new one that replaced it. We wouldn't call this a Criticizing a Viewpoint or Rebutting Critics passage — the author spends far more time discussing evidence supporting the new theory than criticizing the old theory — but these Meta-Structures wouldn't be entirely off-base either. We could even call this a Phenomenon/Explanation passage (phenomenon: rocks of different polarities along mid-ocean ridge; explanation: ocean floor spreading) or Proposing a Hypothesis passage.

Lists: The passage has two sets of lists, making the list the most prominent minor Meta-Structure. First, it provides two new discoveries that led to the development of the new belief (P1, S3; P2, S1). Second, it provides three lines of evidence that support a theory related to the second new discovery (P3, S2-S4). These lists and their elements will likely feature heavily in the questions.

Last Thoughts?

The description of polarity, magnetite, ocean peaks, structurally weak zones, magnetic variations, etc … there is a lot of science in this passage. As such, we're going to have to rely heavily on the passage and our notes to help us answer questions asking about those details, as there's no way we can digest it all in the time we have to read the passage itself.

Question prompt

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

Credited answer: A

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 question asks us to infer, based on the entire passage, a statement that must be true. Such questions can be very challenging. These questions provide little indication as to the topic of the correct answer or where it’ll show up in the passage. Moreover, the correct answer probably won't restate something from the passage. Instead, the question will likely require us to draw a connection between a few different pieces of information.We’ll need to rely on our big-picture understanding of the passage to answer these questions. 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 and isn’t reflected in our notes on each paragraph, 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, consistent with the main point, or reflected in our notes, 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
    Submarine basalt found near Remaining source text redacted.
    Why choice A matches the stem

    (A) Is this consistent with the passage's main point or reflected in our notes?

    Yes. This answer is about the age of rocks on the ocean floor, which is reflected in our notes on "stripes of rock" for the second and third paragraphs. Therefore, it's worth checking the passage to determine if this answer choice is supported.

    We could check either the second or third paragraphs to determine that this answer choice is supported. In the second paragraph, we learn about the ocean floor spreading theory, which holds that rocks along the mid-ocean are formed when magma erupts through the mid-ocean ridge and cools to form basalt (P2, S4-S5). Based on this, we could infer that the basalt nearest to the ridge is the youngest and the basalt gets progressively older farther away from the ridge. Since the mid-ocean ridge is in the middle of the ocean, the continents would be the farthest thing away from them, and the rock closest to them would be the oldest rock on the ocean floor.

    The third paragraph provides even more direct support for this answer choice. It says that, "at or near the ridge crest, the rocks are very young, and they become progressively older away from the crest" (P3, S2). Again, since the ridge is in the middle of the ocean, the continents would be the furthest away from the ridge. Therefore, the rocks closest to the continents would be the oldest.

    Therefore, this answer choice is correct. We can justifiably select it and wrap up this passage.

  2. B
    The older a sample Remaining source text redacted.
    Why choice B is not credited

    (B) Is this consistent with the passage's main point or reflected in our notes?

    Our notes discuss basalt's polarity, so — if we didn't already select the correct answer — we may want to check the passage to see if (B) is correct.

    Upon review, however, we'll see that this is a false statement. The passage says that magma locks in its polarity when it cools and solidifies into basalt (P1, S5-S6). It wouldn’t be “locked in” if it changed!

  3. C
    Compass readings are more Remaining source text redacted.
    Why choice C is not credited

    (C) Is this consistent with the passage's main point or reflected in our notes?

    Nope. Neither the main point nor our notes discuss compass readings. So, we should resist any urge to check the passage and eliminate — or at least table — (C).

    Besides, we wouldn't find any support for (C) if we re-read the entire passage. The passage says that magnetite distorts compass readings, and we know it exists on both land and in the sea (P1, S4). However, we don’t know where it’s more common, and we don’t know if there are any other things that distort compass readings, so this answer makes an unsupported comparison.

  4. D
    The magnetic fields surrounding Remaining source text redacted.
    Why choice D is not credited

    (D) Is this consistent with the passage's main point or reflected in our notes?

    Nope. Neither the main point nor our notes mention whether the magnetic fields surrounding magnetite grains weaken over time. So, we should resist any urge to check the passage and eliminate — or at least table — (D).

    Besides, we wouldn't find any support for (D) if we re-read the entire passage. Although we learn that magnetite is a "strongly magnetic mineral" (P1, S4), we never learn whether this magnetic field weakens over time. And since we're able to discern the magnetic polarity of basalt that's millions of years old (P3, S4), it doesn't seem like it could weaken all that much over time.

  5. E
    Any rock that exhibits Remaining source text redacted.
    Why choice E is not credited

    (E) Is this consistent with the passage's main point or reflected in our notes?

    This is tricky! Our notes discuss basalt's polarity, so — if we didn't already select the correct answer — we may want to check the passage to see if (E) is correct.

    Upon reviewing the passage, we'll see that the passage notes that there are two polarities — normal and reversed (P1, S5) As such, it sounds as if the polarity flips back and forth — it doesn’t change to a unique state each time it changes. So, a rock with present-day, "normal" magnetic polarity could have been formed after the latest reversal. But it could have also been formed three reversals ago (Normal > Reversed > Normal), or five reversals ago (Normal > Reversed > Normal > Reversed > Normal), or seven reversals ago, etc.

What this tests

Discussion

  • Why A? 3 replies

    Started by Hunter

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