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Marine archaeologists examining ancient wooden shipwrecks in the Black Sea observed that wrecks resting at depths greater than 150 meters show virtually no degradation from *Teredo navalis* (a wood-boring mollusk), whereas wrecks at shallower depths in the same sea are severely degraded. Because the water in the Black Sea below 150 meters is permanently devoid of dissolved oxygen (anoxic), whereas shallower water contains normal oxygen levels, the archaeologists concluded that the absence of dissolved oxygen is the primary factor preventing the mollusks from colonizing and destroying the deep-water wrecks.

Which of the following, if true, most strengthens the marine archaeologists' argument?

  1. A
    Ancient shipwrights frequently coated the exterior hulls of wooden merchant vessels with thick coats of pitch and resin, substances that temporarily repel wood-boring larvae.
  2. B
    Anaerobic bacteria thriving in the deep waters of the Black Sea generate high concentrations of chemical byproducts that are toxic to most marine invertebrates, including *Teredo navalis*.
  3. Specimens of *Teredo navalis* placed in water samples drawn from below 150 meters in the Black Sea survive and consume wood normally, provided that dissolved oxygen is continuously introduced into the water.Cevap
  4. D
    Metal artifacts recovered from deep-water Black Sea shipwrecks exhibit significantly less oxidative corrosion than comparable metal artifacts recovered from shallow waters.
  5. E
    Every known species of wood-boring organism native to the Mediterranean Sea requires at least double the concentration of dissolved oxygen found in shallow Black Sea waters.

Cevap

The argument is most strengthened by the finding that *Teredo navalis* can survive and consume wood in water drawn from below 150 meters in the Black Sea as long as dissolved oxygen is artificially added.
The correct response demonstrates that when oxygen is artificially supplied to deep Black Sea water, *Teredo navalis* behaves normally. This experimental control eliminates alternative hypotheses (such as toxic minerals, extreme pressure, or salinity differences unique to the deep basin) that could otherwise account for the absence of wood degradation, thereby directly strengthening the conclusion that oxygen deprivation is the operative factor.

Adım Adım Çözüm

1
Analyze the argument's structure, premises, and conclusion.
Premise: Deep-water wrecks (>150m) in the Black Sea lack mollusk degradation and lack dissolved oxygen, whereas shallow wrecks have both. Conclusion: The lack of dissolved oxygen is the primary factor preventing mollusk degradation in deep waters.
Identifying the exact causal link claimed by the author exposes the underlying gap.
2
Identify the primary inferential gap or vulnerability.
The argument assumes that anoxia itself is the cause, overlooking potential confounding variables inherent to deep Black Sea water (e.g., salinity, pressure, temperature, or other chemical inhibitors).
To strengthen a causal claim, one must either eliminate alternative causes, demonstrate the causal mechanism, or show that the effect occurs when the cause is present and vanishes when the cause is absent.
3
Evaluate the answer choices to determine which best bridges this gap.
The statement showing that mollusks flourish in deep Black Sea water when oxygen is introduced isolates oxygen deficiency as the sole barrier, ruling out other chemical or biological deterrents.
This controlled experimental finding directly substantiates the proposed causal relationship.

Anahtar Kavram

Strengthening Causal Attribution by Ruling Out Confounding Variables
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