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Difficulty: HardCentral Ideas

In the hyper-arid, frigid desert of Antarctica's McMurdo Dry Valleys, visible life on rock surfaces is virtually non-existent. Instead, microbial life, dominated by endolithic lichens, colonizes the pore spaces just millimeters beneath the surface of translucent sandstones. Rather than merely surviving in a dormant state, these organisms actively drive physical and chemical weathering processes. By executing cyclic expansion during brief hydration periods and producing oxalic acid, they gradually dissolve cement minerals, causing the sandstone to flake off. While researchers initially theorized that these micro-ecosystems were static relics of past milder climates, recent metabolic monitoring confirms that they function as active, albeit slow, geomorphological agents that continuously reshape the local landscape.

Which choice best states the main idea of the text?

  1. A
    Microbial communities in extreme environments utilize specialized chemical and physical strategies to withstand harsh climatic conditions.
  2. Endolithic lichens in the McMurdo Dry Valleys actively contribute to the alteration and erosion of sandstone rather than remaining passive or dormant.Answer
  3. C
    Endolithic lichens are static remnants of a historical era when Antarctica experienced a much milder and wetter climate.
  4. D
    The physical weathering caused by endolithic lichens will eventually allow larger, visible organisms to colonize the surface of Antarctic sandstones.

Answer

Endolithic lichens in the McMurdo Dry Valleys actively contribute to the alteration and erosion of sandstone rather than remaining passive or dormant.
The correct answer accurately summarizes the central thesis of the passage: endolithic lichens in the McMurdo Dry Valleys actively drive physical and chemical weathering processes in sandstone, serving as active geomorphological agents rather than remaining passive or dormant relics of past climates.

Step-by-Step Solution

1
Analyze the passage to identify the subject and key claims.
The passage discusses endolithic lichens in the McMurdo Dry Valleys of Antarctica and describes how they perform physical and chemical weathering on sandstones, acting as active geomorphological agents.
Understanding the core topic and claims helps isolate the main idea from supporting details or incorrect theories.
2
Evaluate the author's final conclusion or refinement of earlier ideas.
The text refutes the initial theory that the micro-ecosystems are static remnants of past milder climates, confirming instead that they actively shape the local landscape.
Identifying the author's stance on the activity of these lichens is critical to choosing the correct central idea.
3
Compare the options against the primary focus of the text.
The statement describing the lichens' active contribution to sandstone weathering is the most accurate and comprehensive summary of the passage.
This step ensures that the selected choice reflects the whole passage rather than focusing on a detail, an outdated hypothesis, or an overgeneralization.

Key Concept

Identifying the central idea of a passage by separating primary claims from secondary details or outdated theories.
Estimated Time:2m 0s
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