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Difficulty: EasyInferences and Implicit Meaning

Until recently, marine biologists assumed that deep-sea hydrothermal vent communities relied exclusively on chemosynthetic bacteria utilizing hydrogen sulfide emitted directly from vent chimneys. However, recent sediment analysis near dormant vent fields revealed trace deposits of organic carbon isotope ratios that match those produced by methane-oxidizing archaea rather than sulfur-oxidizing bacteria. Because these isotopic signatures were found in sediment layers deposited thousands of years after vent fluid discharge had ceased, researchers hypothesize that microbial ecosystems can persist around extinct hydrothermal structures far longer than previously thought. The persistence of these communities depends not on active thermal plumes, but on the slow diffusion of trapped subsurface methane through porous volcanic rock. Consequently, estimates of total biological productivity in the abyssal zone may need to be revised upward, as non-eruptive vent sites cover vast expanses of the ocean floor previously regarded as biological deserts.

Which of the following can be inferred from the passage regarding non-eruptive hydrothermal vent sites?

  1. They are capable of sustaining specific microbial communities even after active fluid discharge from vent chimneys has stopped.Answer
  2. B
    They produce greater total biological output per square meter than active hydrothermal vent fields.
  3. C
    They rely primarily on sulfur-oxidizing bacteria that metabolize hydrogen sulfide plumes.
  4. D
    They completely block subsurface methane from diffusing through surrounding porous volcanic rock.
  5. E
    They were widely recognized as primary centers of deep-sea biological activity prior to recent sediment analyses.

Answer

Non-eruptive hydrothermal vent sites are capable of sustaining specific microbial communities even after active fluid discharge from vent chimneys has stopped.
The correct response accurately synthesizes the passage's statement that carbon isotope signatures from methane-oxidizing archaea were present in sediment deposited long after vent fluid discharge ceased, showing that microbial life can continue at these sites after active vent emissions stop.

Step-by-Step Solution

1
Identify the key evidence in the passage regarding non-eruptive vent sites.
The passage states that isotopic signatures of methane-oxidizing archaea were found in sediment layers deposited 'thousands of years after vent fluid discharge had ceased.'
This direct textual connection shows that microbial life persists long after active emissions end.
2
Evaluate the underlying mechanism supporting this persistence.
The text mentions that persistence relies on the 'slow diffusion of trapped subsurface methane through porous volcanic rock.'
This confirms that active plumes are not required to support these specific microbial ecosystems.
3
Match the synthesized evidence to the valid implicit conclusion.
The statement that non-eruptive sites can sustain microbial communities without active fluid discharge logically follows directly from the passage facts.
An inference on the GRE must be strictly supported by passage facts without requiring outside assumptions.

Key Concept

Drawing valid implicit conclusions directly supported by stated evidence without unwarranted extrapolation.
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Topics

Inferences and Implicit Meaning

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