PrepTest 156

[lcid:3720] Prep Test 156 LSAT — Reading Comp — S1 Reading comp

Passage

 Discovered in 1993, the site known as Ukhaa Tolgod, in the Gobi desert of Mongolia, is one of the world's Remaining source text redacted.
Passage walkthrough
Passage Summary

Topic:
Science

Paragraph 1

  • Paragraph note
    • Phenomenon, explanation, evidence it's wrong
  • Views, minor Meta-Structures, and the author's attitude
    • Phenomenon - Ukhaa Tolgod has very well preserved fossils
    • Old Explanation - Big, sudden sandstorms buried animals
    • New Evidence - Geological formations - Sandstorm hypothesis wrong


Paragraph 2

  • Paragraph note
    • New evidence/geological formations
  • Views, minor Meta-Structures, and the author's attitude
    • 3 types of sandstone
      • Tilted layers, sorted by particle size = wind - Footprints, no fossils
      • Tilted layers, not sorted = wind - No fossils
      • No layers, pebbles = not wind - All the fossils


Paragraph 3

  • Paragraph note
    • Explanation for third layer
  • Views, minor Meta-Structures, and the author's attitude
    • Not wind, but water from heavy rains → sudden debris flow
    • New explanation - Sudden debris flow from rain, not wind


Paragraph 4

  • Paragraph note
    • Cause of sandslides
  • Views, minor Meta-Structures, and the author's attitude
    • Cause - Not well understood
    • Evidence - Clay plays a role, with dunes and vegetation also relevant
    • Implication - If sandslide explanation correct, then desert not sterile but had dunes/plants/rain


Main Point:

New evidence suggests sandslides caused by sudden, heavy rains — rather than sandstorms caused by wind — may have preserved Ukhaa Tolgod fossils.



Key Lines?

P1, S2 - Phenomenon
P1, S3 - Old Explanation
P1, S4 - Evidence suggests Old Explanation is wrong
P3, S3 - New Explanation
P4, S1 - Cause of New Explanation not fully understood
P4, S7 - Implication of New Explanation



Meta-Structure?

Old Explanation/New Explanation (or Phenomenon/Explanation): The passage opens with a description of an area with unexpectedly well-preserved fossils. While that doesn't necessarily establish a Meta-Structure, we know that Science passages often fall into the Phenomenon/Explanation Meta-Structure, and the "extraordinar[y]" nature of these fossils suggests that the passager might head in that direction. Paragraph 1, Sentence 3 (P1, S3) reinforces this prediction, as the author raises an explanation: the preservation was "due to" immense, sudden sandstorms. At this point, we might think that this is a Phenomenon/Explanation passage. But then the author goes in a different direction, claiming that evidence suggests the sandstorm explanation is wrong and a new explanation is warranted. The author eventually elaborates on this new explanation in paragraph 3: sandslides, rather than sandstorms, preserved the fossils.



The third paragraph's alternative explanation suggests that the author uses an Old Explanation/New Explanation Meta-Structure (though we could still consider it a Phenomenon/Explanation passage, only with this added wrinkle). In the former Meta-Structure, the author's preferred explanation is the main point; in the latter, it's the author's opinion on the new explanation. Here, the author is the one presenting the new explanation, though the author may not be 100% committed to it (note the noncommittal language in P3, S3 — "could have trapped"; and P4, S7 - "If the animals…"). So the main point is the new explanation, though we have to be careful not to oversell how committed the author is to that explanation.



Causality: Outside of the typically causal nature of a Phenomenon/Explanation passage (in which the explanation is generally causal, as it is here), the author spends a lot of time walking through the causal chain of events that may lead to a sandslide in P4. We probably don't want to get too bogged down with understanding and memorizing it as we read. Still, a prudent test taker would note that P4 is a cause-and-effect-focused paragraph to help answer any questions about P4 or the possible causes of a sandslide.



Comparison: the author spends P2 comparing the different types of sandstones and the evidence found at each site of Ukhaa Tolgod to build to her intermediate conclusion (the sandstorm hypothesis is probably mistaken). These comparisons could feature in a question, and they play into the role of P2, which very well could itself be a question (see "Last Thoughts?", below).



Last Thoughts?

Two things, both about the second paragraph ...



First, it's important to understand the role of that paragraph in the passage's overall organization. P2 and P1 are closely tied. P1 cites "geological formations" as new evidence that the sandstorm hypothesis (the Old Explanation) is probably wrong. The sandstone at the site, discussed in P2, are those "geological formations."



Second, it's important to understand how the author uses this evidence to undermine the old hypothesis. The author brings up three layers of sandstone and highlights similarities and differences between them. Crucially, it's only the third layer that contains fossils. The first layer explicitly doesn't contain fossils, and the second layer implicitly doesn't since "all the vertebrate skeletal fossils" are found in the third layer. Wind caused the first two layers, but wind couldn't have caused the third. Since the fossils are all in the third layer, wind/sandstorms cannot explain why the fossils are "extraordinarily well preserved." Ergo, something else must have preserved those fossils. Understanding this argument will likely play a role in answering at least a few questions!

Question prompt

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

Credited answer: D

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

Question Type

Science

Answer choices

  1. A
    Some scientists have long Remaining source text redacted.
    Why choice A is not credited
    (P4, S7) There are many problems with this answer choice. The most glaring issue is the absence of any reference to the Ukhaa Tolgod fossils, the central topic of this passage. Additionally, although the last paragraph brings up "unusually heavy rainfall" in its discussion of the sandslides, there's no indication that scientists have for many years believed this region experienced abundant rainfall. Finally, this answer focuses on the viewpoint of some scientists, which will not be the main point in a passage where the author takes a stance.
  2. B
    Though the causes of Remaining source text redacted.
    Why choice B is not credited
    (P4, S1-2) Like (A), this answer choice forgets to bring up the fossils in Ukhaa Tolgod, the central topic of this passage. Moreover, this answer choice misdescribes the claims made in the fourth paragraph. The author discusses what may have caused the sandslides in the fourth paragraph but never suggests that scientists have fully endorsed that explanation (in fact, the first sentence of that paragraph suggests there's no settled explanation).
  3. C
    Investigations of geological formations Remaining source text redacted.
    Why choice C is not credited
    This answer reflects a Phenomenon/Old Explanation/New Explanation passage, but it doesn't focus on the right phenomenon or explanation! The central phenomenon is the extraordinary preservation of certain fossils, not the landscape of the Gobi desert in the past. Rather than describe the main point, this answer choice focuses on an ancillary issue. (In all likelihood, this answer choice was written to entice test-takers who reflexively assume the last sentence is the passage's main point.)
  4. D
    Geological evidence suggests that Remaining source text redacted.
    Why choice D matches the stem

    Question Type:
    Main Point

    Strategy Overview:
    Reiterate the main point as we summarized it after reading through the passage, then find the answer that best matches with it

    Answer Anticipation/Relevant Lines:
    As discussed in the "Meta-Structure" section above, this passage utilizes an Old Explanation/New Explanation Meta-Structure. In such a Meta-Structure, the author's opinion on the new explanation is the main point. Here, the author endorses the new explanation, but she's not 100% committed to it (see P3, S3 - "could have trapped"; and P4, S7 - "If the animals…"). So the main point is the new explanation, though we have to be careful not to oversell how committed the author is to it:

    New evidence suggests sandslides caused by sudden, heavy rains — rather than sandstorms caused by wind — may have preserved Ukhaa Tolgod fossils.

    Note the key verb here, "suggests," which implies agreement but a lack of certainty.

    Answer Choice Explanation:
    (P1, S2-3; P3, S3) This answer reflects both the phenomenon that the passage is designed to explain and the new and old explanations offered. The passage sets out to explain why Ukhaa Tolgod has extraordinarily well-preserved fossils. After dismissing the hypothesis that it was caused by immense, sudden sandstorms, the author pivots to say that new evidence points to sandslides, though not with 100% certainty ("could have trapped"; "If the animals"), reflected in this answer's use of "suggests." This answer accurately describes the view the author wants to prove in this passage, so it is correct.

    Key Takeaway:
    The Meta-Structures help us understand the main point and overall direction of the argument. However, there's considerable overlap between the Meta-Structures, and many ways to stitch together the Structures. Rather than think of the Meta-Structures as discrete items on a list, think of each as composed of elements that are repeatedly important in RC passages. Some elements go together more frequently than others, and some more associated with certain topics, but the LSAT can always mix and match them in unexpected ways! Here, it took a Phenomenon/Explanation passage and added on an Old Explanation/New Explanation Meta-Structure — and all of those elements showed up in the correct answer.

  5. E
    The search for fossilized Remaining source text redacted.
    Why choice E is not credited
    The key scientific question that the passage sets out to answer isn't about the formation of sandstone, but rather about what those formations say about the extraordinary preservation of the fossils. This answer therefore misses the mark!

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