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
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
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)
Radiocarbon dating is not examined on a “step-by-step” basis in the rest of the passage.
0%
b
an established procedure ██ █████ █ ███ █████████ ████ ████ ██ ████████
This best capture the purpose. We’re introduced to radiocarbon dating, and in the rest of the passage a new procedure (lichenometry) is compared to it.
The author doesn’t suggest that radiocarbon dating is an outdated procedure. Also, the rest of the passage isn’t concerned with showing that radiocarbon is useful in some situations; it’s about telling us about a new method.
1%
d
a traditional procedure ████ ████ ████ ██ ██████████ ████ █████ ███████████ ██████████
The passage doesn’t contrast radiocarbon dating with other “traditional” procedures. Lichenometry is a new procedure.
0%
e
a popular procedure ████ ████ ████ ██ █████ ██ ████ ████████ ██ █████████ ███████████ █████ █ ██████████
The passage doesn’t show that radiocarbon dating has reached incorrect conclusions about something.
0%
Difficulty
98% of people who answer get this correct
This is a low-difficulty question.
It is somewhat easier than other questions in this passage.
CURVE
Score of students with a 50% chance of getting this right
25%120
123
75%132
Analysis
Purpose of paragraph
Purpose of paragraph
Stems that ask us to describe the purpose of a paragraph within the passage's broader structure, often in abstract language (e.g. "to offer evidence in support of the contention that...").
An umbrella tag marking questions that test our understanding of the passage's overall structure (e.g. Main point, Purpose of paragraph, Meaning in context, Describe organization).
