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

The observations reported in 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

Answer choices

  1. A
    In order to theorize Remaining source text redacted.
    Why choice A matches the stem

    Question Type:
    Parallel Reasoning/Argument Structure

    Strategy Overview:
    Review the relevant observations, figure out the function they serve in the argument in that paragraph, and then use that generalization to help find an analogous answer.

    Answer Anticipation/Relevant Lines:
    Note that this question stem tells us to find an answer that "serve[s] a function" similar to the one in the passage served by the observations. In other words, we should start by approaching this as an Argument Structure question and then find an answer that reflects a different scenario where the same function is served.

    As with any Argument Structure question, we need to consider the relevant line's wider context to understand its role. Here, the observations show up in Paragraph 4, so we should consider that paragraph's role. We noted that it discusses a potential cause of the sandslides, which are central to the alternative hypothesis for Ukhaa Tolgod's well-preserved fossils. So the observations must in some way advance the argument behind this cause.

    Checking the immediate context of the observations, we see that they place a limitation on the clay theory — in modern dunes, clay accumulates "only if" there's a lot of vegetation on the dunes. The passage then goes on to draw an implication from this — if the sandslide hypothesis is correct, then the area must have had plant life and rain at some point in the past.

    So, the observations use modern knowledge to draw an implication about the possible past conditions of the region. Let's find an answer with a similar purpose.

    Answer Choice Explanation:
    This answer involves using a modern observation to draw a conclusion about how something in the past occurred. This has a very similar purpose to the observations regarding "modern sand dunes," which were used to draw a conclusion about Ukhaa Tolgod's past conditions, so it's the correct answer.

    Key Takeaway:
    Note how significant the timeline element was here. The passage used "modern" observations to draw a conclusion about the past, and many answers were wrong because they didn't line up with that. Timelines are important on the LSAT, and using evidence from a different period than the one in which the conclusion is being drawn relies on flawed logic that we've seen many times before.

  2. B
    In order to determine Remaining source text redacted.
    Why choice B is not credited
    This answer features a survey done in the modern era to draw a conclusion about the modern era. It doesn't attempt to explain how something happened in the past. So its purpose is dissimilar to the observations in the second-to-last sentence of the passage, and it is incorrect.
  3. C
    A historian considers some Remaining source text redacted.
    Why choice C is not credited
    This answer describes evidence from the past being used to make a conclusion about past conditions. Therefore, it doesn't have the same function as the observations in the passage. There, modern observations were used to draw conclusions about past events.
  4. D
    As part of an Remaining source text redacted.
    Why choice D is not credited
    This answer is almost the opposite of the passage — past information is used to draw future conclusions. In the passage, present observations were used to draw conclusions about the past.
  5. E
    An archaeologist examines the Remaining source text redacted.
    Why choice E is not credited
    Another answer where the evidence is from the past — preserved objects may still exist, but their preservation occurred in the past. Since this answer choice doesn't have observations of modern phenomena, it's not analogous to the situation in the passage.

What this tests

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