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Difficulty: MediumIdentifying Hypotheses and Beliefs

### Subglacial Lake Heating Models

Scientists are investigating the source of liquid water in Lake Vostok, a large subglacial lake located beneath the East Antarctic Ice Sheet. The air temperature above the ice sheet averages −55∘C-55^\circ\text{C}, yet the water at the bottom of the lake remains liquid. Two hypotheses are proposed to explain this phenomenon:

Geothermal Hypothesis
The primary source of heat is geothermal energy radiating from the Earth's interior through the thin continental crust directly beneath the lake. This constant thermal flux maintains a water temperature of approximately 1∘C1^\circ\text{C} to 3∘C3^\circ\text{C} at the lake bed, preventing the water from freezing. Proponents of this hypothesis believe that the thickness of the overlying ice sheet (4 km4\text{ km}) acts as an insulator, trapping this geothermal heat.

Frictional Hypothesis
The primary source of heat is friction generated by the movement of the ice sheet sliding over the rugged bedrock topography. As gravity pulls the massive ice sheet slowly downhill, kinetic energy is converted into thermal energy at the boundary between the ice and the rock. Proponents of this hypothesis believe that this sliding friction melts the bottom layers of the ice sheet, continuously feeding liquid water into the lake. They suggest that geothermal heat flux in the region is average and insufficient to melt the ice on its own.

Which of the following statements best describes a belief held by the proponents of the Frictional Hypothesis but NOT by the proponents of the Geothermal Hypothesis?

  1. The sliding movement of the ice sheet over bedrock is the primary heat source responsible for the liquid water in the lake.Answer
  2. B
    The overlying ice sheet is thick enough to act as an insulator, keeping geothermal heat from escaping.
  3. C
    Geothermal energy radiating from the Earth's interior is the primary driver of ice melt beneath the ice sheet.
  4. D
    The air temperature above the ice sheet must rise above 0∘C0^\circ\text{C} for subglacial liquid water to form.

Answer

The sliding movement of the ice sheet over bedrock is the primary heat source responsible for the liquid water in the lake.
The correct answer states that the sliding movement of the ice sheet over bedrock is the primary heat source responsible for the liquid water in the lake. According to the passage, this is the central claim of the Frictional Hypothesis. Proponents of the Geothermal Hypothesis do not share this belief; instead, they believe geothermal energy radiating from the Earth's interior is the primary driver.

Step-by-Step Solution

1
Identify the core claim of the Frictional Hypothesis in the passage.
The Frictional Hypothesis states that 'The primary source of heat is friction generated by the movement of the ice sheet sliding over the rugged bedrock topography.'
This establishes the belief that must be represented in the correct choice.
2
Identify the core claim of the Geothermal Hypothesis in the passage.
The Geothermal Hypothesis states that 'The primary source of heat is geothermal energy radiating from the Earth's interior...'
This allows us to rule out beliefs that belong exclusively to the Geothermal Hypothesis or are shared by both.
3
Match the identified Frictional Hypothesis claim with the given options and verify that the Geothermal Hypothesis does not share this belief.
The option stating that sliding movement of the ice sheet over bedrock is the primary heat source matches the Frictional Hypothesis and is rejected by the Geothermal Hypothesis, which attributes the heat to geothermal energy instead.
This confirms the correct option based on the contrasting beliefs.

Key Concept

Identifying and contrasting beliefs and hypotheses in scientific arguments
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Topics

Identifying Hypotheses and Beliefs

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