If the formation of Earth's mantle had been purely a product of core differentiation—whereby heavier elements sink toward the core...
GMAT Expression of Ideas : (Expression) Questions
If the formation of Earth's mantle had been purely a product of core differentiation—whereby heavier elements sink toward the core and lighter elements rise—the upper mantle would be depleted of heavy siderophile elements. Siderophiles are much more abundant in the mantle than predicted in that model, however. ________ extraterrestrial material containing siderophiles, likely from asteroid or comet impacts, almost certainly accreted to Earth following core differentiation.
Which choice completes the text with the most logical transition?
That said,
Hence,
For example,
Likewise,
Step 1: Decode and Map the Passage
Passage Analysis Table
| Text from Passage | Analysis |
|---|---|
| "If the formation of Earth's mantle had been purely a product of core differentiation—whereby heavier elements sink toward the core and lighter elements rise—the upper mantle would be depleted of heavy siderophile elements." |
|
| "Siderophiles are much more abundant in the mantle than predicted in that model, however." |
|
| "[MISSING TRANSITION]" |
|
| "extraterrestrial material containing siderophiles, likely from asteroid or comet impacts, almost certainly accreted to Earth following core differentiation." |
|
Passage Architecture & Core Elements
Main Point: Earth's mantle contains more heavy elements than core differentiation alone would predict because extraterrestrial material was added later.
Argument Flow: The passage starts with a scientific model that predicts low concentrations of certain elements in Earth's mantle. It then reveals that reality doesn't match this prediction—there are actually much higher concentrations. The final sentence explains this discrepancy by proposing that space impacts added these elements after the initial formation process.
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
- The relationship between the sentences is crucial here. Before the blank, we learn there's a problem: the mantle has way more siderophiles than the core differentiation model would predict. After the blank, we get a solution: extraterrestrial impacts brought these elements to Earth after core formation.
- The logical relationship is cause-and-effect or conclusion-drawing. Because we have this unexplained abundance of elements, therefore we conclude that space impacts must have added them later.
- So the right answer should signal a logical conclusion or consequence—something that shows the second sentence follows as a natural result from the problem identified in the first part.
That said,
- "That said" typically introduces a qualification or contrast to what was just stated. Here we need a connector showing logical consequence, not contrast or qualification. The second sentence doesn't contradict or qualify the abundance observation—it explains it.
Hence,
- "Hence" signals a logical conclusion drawn from preceding information. Fits perfectly: the abundance of siderophiles (contrary to the model) leads to the conclusion that extraterrestrial material must have been added. Creates the clear cause-effect relationship between the problem and its explanation.
For example,
- "For example" would introduce a specific instance of something general mentioned before. The second sentence isn't providing an example of siderophile abundance—it's explaining why that abundance exists.
Likewise,
- "Likewise" suggests a parallel or similar situation to what was just described. No parallel is being drawn here—we're moving from observation to explanation. The relationship is explanatory, not comparative.