To investigate the history of plate subduction—when one of Earth's tectonic plates slides beneath another—Sarah M. Aarons and colleagues compared...
GMAT Information and Ideas : (Ideas) Questions
To investigate the history of plate subduction—when one of Earth's tectonic plates slides beneath another—Sarah M. Aarons and colleagues compared ancient rocks from the Acasta Gneiss Complex in Canada to modern rocks. Using isotope analysis, the researchers found that Acasta rocks dating to about 4.02 billion years ago (bya) most strongly resemble modern rocks formed in a plume setting (an area in which hot rocks from Earth's mantle flow upward into the crust). By contrast, they found that Acasta rocks dating to about 3.75 bya and 3.6 bya have an isotope composition that is similar to that of modern rocks formed in a subduction setting. Aarons's team therefore concluded that ______
Which choice most logically completes the text?
Step 1: Decode and Map the Passage
Passage Analysis Table
| Text from Passage | Analysis |
|---|---|
| "To investigate the history of plate subduction—when one of Earth's tectonic plates slides beneath another—Sarah M. Aarons and colleagues compared ancient rocks from the Acasta Gneiss Complex in Canada to modern rocks." |
|
| "Using isotope analysis, the researchers found that Acasta rocks dating to about 4.02 billion years ago (bya) most strongly resemble modern rocks formed in a plume setting (an area in which hot rocks from Earth's mantle flow upward into the crust)." |
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| "By contrast, they found that Acasta rocks dating to about 3.75 bya and 3.6 bya have an isotope composition that is similar to that of modern rocks formed in a subduction setting." |
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The evidence shows a clear timeline shift: rocks from 4.02 billion years ago looked like plume formations, but rocks from 3.75 and 3.6 billion years ago looked like subduction formations. This suggests that somewhere between 4.02 and 3.75 billion years ago, subduction processes started occurring.
Step 2: Interpret the Question Precisely
This is a fill-in-the-blank question asking us to choose the best logical connector. The answer must create the right relationship between what comes before and after the blank.
Step 3: Prethink the Answer
- Evidence shows a clear timeline shift: rocks from 4.02 billion years ago looked like plume formations, but rocks from 3.75 and 3.6 billion years ago looked like subduction formations
- This suggests that somewhere between 4.02 and 3.75 billion years ago, subduction processes started occurring
- Claims subduction began no later than 3.75 bya
- This directly follows from the evidence that 3.75 bya rocks resemble modern subduction rocks
- Claims subduction replaced plume formation by 4.02 bya
- This contradicts the evidence showing plume-like conditions at 4.02 bya
- Makes claims about the majority of Acasta rocks
- Goes beyond what the evidence supports
- Suggests rocks are more recent than previously thought
- Doesn't address the main finding about the transition from plume to subduction processes