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Difficulty: MediumCause-and-Effect Relationships

Passage:

In the subarctic tundra, the rise in global temperatures has initiated a self-reinforcing ecological cycle. As atmospheric warming increases, it accelerates the thawing of ancient permafrost layers that have remained frozen for millennia. Within this newly thawed soil, dormant organic matter becomes accessible to soil microbes. These microbes decompose the organic material, releasing carbon dioxide and methane gases as byproducts. As these greenhouse gases escape into the atmosphere, they trap additional thermal radiation. Consequently, this trapped heat intensifies regional warming, which in turn hastens the thaw of adjacent permafrost zones.

Based on the passage, arrange the following events in order of cause to effect, starting with the initial cause and ending with the final consequence of the feedback loop.

  1. 1The thawing of ancient permafrost exposes previously frozen organic matter.
  2. 2Soil microbes decompose the newly accessible organic material.
  3. 3Carbon dioxide and methane are released into the atmosphere as byproducts.
  4. 4Trapped heat from atmospheric greenhouse gases accelerates further permafrost thaw.

Answer

The correct sequence starts with permafrost thawing, which exposes organic matter. This allows microbes to decompose the material, releasing greenhouse gases that trap heat and further accelerate the thawing process.
The correct order follows the logical progression of the feedback loop: first, thawing occurs, exposing organic matter; second, microbes decompose this matter; third, greenhouse gases are released; and fourth, these gases trap heat to accelerate further thawing.

Step-by-Step Solution

1
Identify the initial event in the causal chain from the text.
The thawing of permafrost layers exposes organic material.
The passage states that thawing permafrost makes organic matter accessible to microbes, indicating thawing is the necessary first step.
2
Determine the direct consequence of the organic matter becoming accessible.
Microbes decompose the organic matter.
The text directly states that microbes decompose the newly accessible organic material.
3
Identify the byproduct of this microbial decomposition.
Greenhouse gases (carbon dioxide and methane) are released.
The passage notes that the microbes release carbon dioxide and methane as byproducts during decomposition.
4
Trace the final effect of the released gases on the environment.
Trapped heat from these gases intensifies regional warming and accelerates thawing.
The text explains that the escaped gases trap thermal radiation, which intensifies warming and hastens further permafrost thaw, completing the feedback loop.

Key Concept

Understanding sequential cause-and-effect relationships and feedback loops in a passage.
Estimated Time:1m 30s
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Topics

Cause-and-Effect Relationships

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