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Difficulty: EasyExplicit Causal Relationships

Based on the passage, arrange the following events in the causal sequence in which they occur, from the initial cause to the final effect.

Passage:
Recent studies of Arctic ecosystems have illuminated the complex feedback loops triggered by climate change. The massive emission of methane—a greenhouse gas significantly more potent than carbon dioxide—is of particular concern to climatologists. These methane emissions are directly generated by the metabolic breakdown of ancient organic material. This decomposition occurs because microbes are finally able to access and consume vast quantities of organic matter. Crucially, this organic matter, which had been locked in ice for millennia, is exposed to microbial life when initial atmospheric warming causes the expansive permafrost layers across the tundra to thaw.

  1. 1The thawing of expansive permafrost layers
  2. 2The exposure of millennia-old organic matter to microbes
  3. 3The metabolic breakdown of organic material by microbes
  4. 4The generation of massive methane emissions

Answer

The correct sequence starts with the permafrost thawing, which exposes organic matter to microbes. The microbes then break down the material, which finally generates methane emissions.
The correct causal sequence traces the events from the initial environmental trigger to the final atmospheric consequence. The passage explicitly states that atmospheric warming causes permafrost to thaw. This thawing exposes trapped organic matter to microbes. The microbes then metabolically break down this newly accessible material. Finally, this decomposition process directly generates methane emissions.

Step-by-Step Solution

1
Analyze the passage to identify the foundational cause of the entire process.
The passage states that the organic matter is exposed 'when initial atmospheric warming causes the expansive permafrost layers... to thaw.'
Finding the root cause establishes the starting point (first event) of the causal chain.
2
Identify the immediate consequence of the permafrost thawing.
The thawing means that the 'organic matter... is exposed to microbial life.'
Tracing the direct effect of the thaw provides the second event in the sequence.
3
Determine what occurs once the organic matter is exposed.
The passage explains that once accessed, 'decomposition occurs because microbes are finally able to access and consume' the material.
This establishes the third event in the causal chain.
4
Identify the final result of the decomposition process.
The text notes that 'methane emissions are directly generated by the metabolic breakdown.'
This confirms the final event, completing the causal sequence from initial trigger to ultimate consequence.

Key Concept

Explicit Causal Relationships
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Explicit Causal Relationships

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