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Question

Difficulty: MediumWeaken

Anthropologist: The discovery of ceremonial obsidian blades in the ruins of the agrarian Vaelian civilization, which flourished 3,000 years ago, proves that the Vaelians engaged in long-distance commerce. The only known geological source of this specific type of obsidian is Mount Cinder, located nearly 400 miles away from the Vaelian settlements. Given that the Vaelians were deeply tied to their farmlands and lacked the means for long-distance travel, they must have acquired these blades by trading with nomadic groups.

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

  1. Geological surveys indicate that a massive prehistoric river once flowed directly from Mount Cinder to the Vaelian valley, depositing large quantities of obsidian boulders throughout the region.Answer
  2. B
    The Vaelians were actually highly mobile and frequently organized expeditions that traveled hundreds of miles to gather rare materials.
  3. C
    Artifacts from the Vaelian civilization have been discovered in the excavated encampments of ancient nomadic groups that routinely traveled near Mount Cinder.
  4. D
    In many ancient cultures, ceremonial items were passed down through numerous generations rather than being newly acquired by each generation.
  5. E
    Obsidian blades represented a tiny percentage of all Vaelian tools, even though the absolute number of blades found was quite large.

Answer

The option stating that a massive prehistoric river deposited obsidian boulders throughout the Vaelian region.
The anthropologist's argument relies on the assumption that if the Vaelians couldn't travel to the obsidian source, they must have relied on other humans (nomads) to bring it to them. The correct answer introduces a third, unconsidered possibility: natural geological forces (a prehistoric river) transported the raw material to the Vaelians' location long before they needed it. If the stones were already in their valley, no trade network was necessary, which destroys the author's conclusion.

Step-by-Step Solution

1
Identify the conclusion of the argument.
Conclusion: The Vaelians must have acquired the obsidian blades by trading with nomadic groups.
This establishes the core claim that the question asks you to undermine.
2
Identify the premises supporting the conclusion.
Premises: (1) Obsidian blades were found in Vaelian ruins. (2) The only source of this obsidian is 400 miles away. (3) Vaelians could not travel long distances themselves.
Understanding the evidence reveals the logical gap.
3
Identify the logical gap (assumption) between the premises and the conclusion.
The anthropologist assumes that human transport (specifically trade) is the ONLY way the obsidian could cross the 400-mile distance.
Arguments are weakened by exposing and attacking their unstated assumptions.
4
Evaluate the options to find one that attacks this assumption.
The option describing a prehistoric river shows that natural geological forces, not human trade, could have moved the stones, severing the link between the premises and the conclusion.
Providing a plausible alternate explanation is the most common way to weaken a causal or explanatory argument.

Key Concept

Alternative Explanations in Argument Evaluation
Estimated Time:1m 30s
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