Reading comp PrepTest 133 · Section 4 · Question 20

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.

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.

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.