Question 75·Hard·Text Structure and Purpose
Geologist Melissa Kipp’s 2008 core samples from Lake Viel revealed an unexpectedly dense band of zircons, apparently corroborating the prevailing view that a nearby volcanic eruption roughly 10,000 years ago had sprinkled mineral-rich ash across the basin. Subsequent isotopic work by Raul Peres, however, dated the zircons far earlier than the eruption, undermining that interpretation. Peres suggested that retreating glaciers might instead have conveyed the minerals, but that hypothesis fails to account for the abruptness of the zircon layer’s lower boundary. Kipp now advances a third possibility: a series of small, quake-triggered landslides from the surrounding cliffs, occurring in quick succession, could have concentrated the zircons in a single, geologically rapid episode.
Which choice best describes the overall structure of the text?
For "overall structure" questions, first quickly underline or mentally note what each sentence is doing (e.g., observation → explanation → new evidence → critique → new explanation). Then, in your own words, sum up the sequence in 2–3 short phrases. Compare that rough outline against each answer choice and eliminate options that (1) change the order of ideas, (2) add a purpose or conclusion not stated in the passage (like policy recommendations or calls for more research), or (3) misrepresent how strongly the author accepts or rejects each idea. Choose the option that closely matches both the content and the order of the passage’s moves.
Hints
Break the paragraph into parts
Read the passage one sentence at a time. For each sentence, ask: is it presenting evidence, supporting an idea, questioning an idea, or offering a new idea?
Notice changes in interpretation
Pay attention to transition words like "however" and "but." How do these words signal shifts from one explanation or viewpoint to another?
Compare how each explanation is treated
Does the passage treat all explanations as equally strong, or does it clearly show that some are undermined or incomplete while another is put forward afterward?
Watch for conclusions or calls to action
Check if the passage ever says something like "more research is needed," "no explanation is possible," or urges any real-world policy changes. Eliminate any answer choice that adds a conclusion or purpose that isn't actually stated.
Step-by-step Explanation
Identify what the first sentence is doing
Read the first sentence:
"Geologist Melissa Kipp’s 2008 core samples from Lake Viel revealed an unexpectedly dense band of zircons, apparently corroborating the prevailing view that a nearby volcanic eruption roughly 10,000 years ago had sprinkled mineral-rich ash across the basin."
Here, the author
- describes a new observation (dense band of zircons), and
- says it seems to support an already accepted explanation (the “prevailing view” of a volcanic eruption spreading ash).
So the structure starts with evidence that appears to back up a widely accepted explanation.
See how the second sentence changes that first explanation
Look at the second sentence:
"Subsequent isotopic work by Raul Peres, however, dated the zircons far earlier than the eruption, undermining that interpretation."
This introduces new findings (isotopic dating) that show the zircons are much older than the eruption. That directly contradicts the earlier “prevailing view” explanation.
So structurally, we now have: first an explanation that seems supported, then new evidence that shows this explanation is likely wrong.
Track the role of the third sentence
Now read the third sentence:
"Peres suggested that retreating glaciers might instead have conveyed the minerals, but that hypothesis fails to account for the abruptness of the zircon layer’s lower boundary."
Here, Peres offers another possible explanation (glaciers carrying minerals). The author immediately points out a problem: it fails to explain a key feature (the abrupt lower boundary). That means the second explanation is evaluated and found inadequate or incomplete.
See what the final sentence contributes and match the full sequence
The last sentence says:
"Kipp now advances a third possibility: a series of small, quake-triggered landslides from the surrounding cliffs, occurring in quick succession, could have concentrated the zircons in a single, geologically rapid episode."
So the author now presents another (third) explanation for the same zircon layer, after showing problems with the first two.
Putting all four sentences together, the structure is:
- Evidence that initially seems to support a widely accepted explanation.
- New data that contradicts that explanation.
- A second explanation that is considered but found unsatisfactory.
- A third explanation that is proposed as a better fit.
This sequence is exactly described by answer choice D: "It introduces evidence that appears to support a widely accepted explanation, presents new findings that contradict that explanation, evaluates a second explanation and finds it inadequate, and then proposes a third explanation."