PrepTest 132

Topic: Science

Paragraph 1

• Paragraph note
  • Traditional approach to dating earthquakes (radiocarbon dating of carbon 14 isotopes in organic material near faults)
• Views, minor Meta-Structures, and the author's attitude
  • Old approach:
    • Radiocarbon dating (of carbon 14 isotopes) of organic material trapped in sediments that show evidence of having shifted near fault lines (first through third sentence)
    • This can show the location and frequency of past earthquakes and the likelihood of future earthquakes (last sentence)

Paragraph 2

• Paragraph note
  • New approach to dating earthquakes (lichenometry — measuring lichen growth along rocks)
• Views, minor Meta-Structures, and the author's attitude
  • New approach:
    • Bull and Brandon developed lichenometry, which involves measuring lichen growth along rocks exposed by rockfalls following earthquakes (first through fourth sentences)
    • The number of rockfalls can show how strong the earthquake was and the location of rockfalls can help map the earthquake's epicenter (seventh and last sentences)
  • Example of lichen's slow and steady growth:
    • North American lichen, which grows 9.5 mm/year (fifth sentence)
  • Author's attitude: "provides direct evidence" (sixth sentence); "would imply" (seventh sentence); "can then be determined" (last sentence)

Paragraph 3

• Paragraph note
  • Author on disadvantages of radiocarbon dating (not accurate in last 300 years, as the environment affects isotopes) and Bull/Brandon's requirements for lichenometry (minimize/factor disturbances like snow, shade, wind)
• Views, minor Meta-Structures, and the author's attitude
  • Author's view:
    • Lichenometry has distinct advantages over radiocarbon dating, the latter of which is only accurate to within +/- 40 years and not of much use in the past 300 years (first through third sentences)
  • Bull and Brandon's view:
    • Lichenometry is accurate to within +/- 10 years and best in the past 500 years, but one needs to take into account the factors that can speed or slow lichen growth, like snow, wind, and shade (fifth through last sentences)
  • Cause-and-effect relationships:
    • Radiation on the Earth's upper atmosphere causes the amount of carbon 14 isotope to vary (second sentence)
    • Heavy radiation fluctuation in the last 300 years causes radiocarbon dating during this era to be useless (third sentence)
    • Snow avalanches and other disturbances can cause lichen growth to slow down (last sentence)
    • Shade and wind causes lichen growth to speed up (last sentence)
  • Author's attitude: "distinct advantages" (first sentence); "accurate only to within plus or minus 40 years" (second sentence); "fluctuated greatly" (third sentence); "of little value" (third sentence)

Main Point: Even though it requires careful site selection and calibration, lichenometry, a new technique for dating past earthquakes, has several advantages over the traditional radiocarbon dating technique.

OldApproach/New Approach: This passage fits the Old Approach/New Approach Meta-Structure like a glove. In such a passage, the author will typically start by describing an old way of doing something or thinking about something. Often, this is referred to as the "traditional" approach or theory). The author will then describe a new, alternative way of doing or thinking about that same thing. Usually, the author prefers the new approach.

That's what happens here. The author introduces the "usual[]" technique in the first paragraph before shifting to the new technique in the second. When a passage utilizes this Old Approach/New Approach Meta-Structure, the author's opinion on the new approach is usually the main point. Here, the author feels that it has "distinct advantages" over the old technique, so we should ground our understanding of the main point in that view.

Be careful with the end of this passage, starting in the fifth sentence of the last paragraph (beginning with "They note"). The author pivots here, stating that Bull and Brandon note some limitations on lichenometry — careful site selection and calibration. However, that doesn't undercut the author's claim that lichenometry has "distinct advantages" over radiocarbon dating, so we shouldn't feel as if this section is enough to make the author want to abandon the practice. That opening line of the third paragraph is still the clearest statement of the author's opinion.