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Marine Biologist: Deep-sea coral colonies situated adjacent to hydrothermal vents exhibit significantly faster calcification rates than colonies in non-volcanic regions. Because hydrothermal vents continuously release dissolved iron and silicate compounds into the surrounding water, the high concentration of these specific minerals must be the primary cause of the accelerated growth rates observed in these vent-adjacent corals.

Which of the following, if true, most seriously weakens the marine biologist's argument?

  1. A
    Deep-sea corals living in non-volcanic regions demonstrate increased calcification rates when their environment is supplemented with mineral-rich sediment.
  2. B
    Hydrothermal vents release high levels of sulfur compounds that prevent any iron or silicate compounds from remaining dissolved in surrounding seawater.
  3. In controlled laboratory conditions, deep-sea corals exposed to vent-level concentrations of dissolved iron and silicate compounds exhibit no increase in their calcification rates.Answer
  4. D
    No coral species anywhere in the world can survive without the presence of dissolved silicate compounds in the water column.
  5. E
    Deep-sea coral reefs situated near volcanic vents face a greater threat of physical damage from seismic tremors than reefs in non-volcanic waters.

Answer

The statement showing that deep-sea corals exposed to vent-level mineral concentrations in controlled conditions experience no increase in calcification rates most seriously undermines the argument.
The argument concludes that elevated concentrations of dissolved iron and silicates cause accelerated calcification based solely on the correlation between vent proximity and growth rates. The correct answer weakens this causal claim by providing direct experimental evidence that exposing corals to these exact mineral concentrations does not increase calcification, proving the proposed cause is ineffective.

Step-by-Step Solution

1
Identify the conclusion and premises of the argument.
Premise: Corals near hydrothermal vents calcify faster and vents release high levels of iron and silicate. Conclusion: High mineral concentration is the primary cause of the accelerated calcification.
Isolating the core causal claim reveals the logical gap between observed correlation and inferred causation.
2
Identify the unstated assumption linking the premises to the conclusion.
The author assumes that the elevated mineral levels actually stimulate coral calcification and that no alternative factor unique to the vents is responsible.
Weaken questions require targeting the unstated assumption that makes the causal conclusion vulnerable.
3
Evaluate the answer choices to find new information that severs this causal relationship.
Experimental evidence demonstrating that vent-level concentrations of iron and silicate do not increase calcification rates directly disproves the claimed causal mechanism.
Showing that the hypothesized cause fails to produce the effect under controlled conditions decisively weakens a causal claim.

Key Concept

Causal Reasoning and Severing Causal Mechanisms
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