PrepTest 132 - Section 1 - Passage 1 - Question 8

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To study centuries-old earthquakes and the geologic faults that caused them, seismologists usually dig trenches along visible fault lines, looking for sediments that show evidence of having shifted. ███

Intro topic · Methods for studying causes of past earthquakes

Start by looking for buried sediments that shifted during a possible earthquake

Explain method · Use carbon 14 to back-date when material shifted (i.e., when possible earthquake occurred)

Carbon 14 is a radioactive form of carbon that decays (i.e., turns into a different form of carbon) at a known rate, so the amount of carbon 14 left in something can tell us how old that thing is

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Application of method · Determine details of past earthquakes, predict future earthquakes

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Intro new method · Lichenometry

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Explain new method · Use lichen growth to back-date rockfalls in mountain ranges

Lichens begin growing on rocks after an earthquake causes rockfalls; because they grow at a known rate, the size of a lichen patch on a rock can tell us when that rock first fell

Application of new method · If many rockfalls occurred at the same time, that suggests an earthquake

Earthquake was strongest where the most number of rockfalls occurred

Support for lichenometry · over carbon 14 dating

Carbon 14 dating is less accurate because it can be hard to know how much carbon 14 the material started with (just knowing the rate of carbon 14 decay on its own can't tell us how old that material is)

Limitations of lichenometry · Limited time period, complications related to site selection

Passage Style

Single position

Given the information in the ████████ ██ █████ ███ ██ ███ █████████ █████ ████████████ ██████ ██ ████ ███████████

Question Type

Application

It’s hard to predict the correct answer based only on the question stem, so we’ll have to rely on process of elimination. Let’s keep in mind that lichenometry works by measuring the size of lichens growing on rocks, and that it works best for earthquakes in the past 500 years.

identifying the number ██ █████ █ ██████████ █████ ███ ███████ ██ ███ ████ █████ █████

It’s not clear how lichenometry can help identify the number of times a river has flooded. Lichenometry measures the size of lichens growing on rock. If a river has flooded, it’s not clear how that impacts the lichens.

identifying the age ██ █ ██████████ ████████ ██ █ ██████ ████ █████ ████ █████████ ██ █████ ███

It’s not clear how lichenometry can help identify the age of a skeleton. The technique measures the size of lichens growing on rock.

identifying the age ██ ██ ███████ █████ ███ ██████████ █████████████ ██ ██████████ ███ ███ ███████ █████

It’s not clear how lichenometry can help identify the age of a beach that’s underwater. The technique measures the size of lichens growing on rock.

identifying the rate, ██ ██████████ ███ ████████ ██ █████ █ ███████ ███ ████ ████████ ██ █ ████████ ██████

This is the best answer, because we might be able to identify the rate a glacier has been moving/melting up a mountain valley by measuring lichen growth on the rock that is exposed when the glacier recedes. No other answer involves a measurement that we can make based on lichen growth on exposed rock.

70%

identifying local trends ██ ██████ ████████ █████ ██ █ ██████████ ██████ ████ ███ ████ ████ █████████

It’s not clear how lichenometry can help identify trends in annual rainfall. The technique measures the size of lichens growing on rock. Does rainfall affect lichens? And how? We don’t know.

15%

PrepTest 132 - Section 1 - Passage 1 - Question 8

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