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Difficulty: MediumIdentifying Core Claims and Hypotheses

### The Faint Young Sun Paradox
During the Archean Eon, approximately 3.83.8 to 2.52.5 billion years ago, the Sun’s energy output was only about 70%70\% to 75%75\% of its present-day value. Under these conditions, the Earth should have been completely frozen, yet geological evidence indicates that liquid water and life were present. Scientists debate how Earth maintained a warm climate during this period.

Scientist 1
The early Earth was kept warm primarily by a super-greenhouse effect caused by extremely high levels of carbon dioxide (CO2CO_2) and water vapor (H2OH_2O). Volcanic outgassing released CO2CO_2 at rates up to 100 times greater than today, building an atmosphere with CO2CO_2 levels high enough to prevent global glaciation despite the weaker Sun.

Scientist 2
High CO2CO_2 levels alone could not have prevented glaciation because geochemical evidence from ancient soils limits Archean CO2CO_2 concentrations to levels too low to explain the warmth. Instead, the primary driver of warming was methane (CH4CH_4) produced by early anaerobic microbes. This methane, in combination with moderate CO2CO_2 levels, formed a powerful greenhouse gas mixture that prevented freezing.

Scientist 3
Earth’s temperature was maintained not by an enhanced greenhouse effect, but by a lower planetary albedo (reflectivity). The Archean Earth had much smaller continental landmasses and lacked land plants, meaning less sunlight was reflected back into space. Additionally, fewer biological cloud condensation nuclei existed, resulting in fewer, larger cloud droplets that reflected less solar radiation.

Based on the passage, which of the following statements best describes the core claim of Scientist 2 regarding the prevention of global glaciation during the Archean Eon?

  1. Methane produced by early microbes, alongside moderate carbon dioxide, was the primary greenhouse gas mixture responsible for warming the planet.Answer
  2. B
    A super-greenhouse effect driven solely by volcanic outgassing of high levels of carbon dioxide and water vapor kept the planet warm.
  3. C
    The primary cause of warming was a lower planetary albedo due to smaller continental landmasses and fewer cloud condensation nuclei.
  4. D
    Methane concentrations were kept low by anaerobic microbes, allowing carbon dioxide to dominate the atmosphere and warm the Earth.

Answer

Methane produced by early microbes, alongside moderate carbon dioxide, was the primary greenhouse gas mixture responsible for warming the planet.
The correct answer accurately reflects the hypothesis of Scientist 2. Scientist 2 argues that carbon dioxide levels were too low to prevent glaciation on their own and that methane produced by early anaerobic microbes, mixed with moderate carbon dioxide, was the primary driver of warming.

Step-by-Step Solution

1
Identify the target scientist and locate their section in the passage.
The target is Scientist 2. The relevant section is the paragraph labeled 'Scientist 2'.
This establishes where to find the evidence needed to answer the question.
2
Analyze the claims made by Scientist 2 regarding Archean warming.
Scientist 2 states that carbon dioxide was insufficient on its own, and that methane produced by early anaerobic microbes, along with moderate carbon dioxide, formed the greenhouse mixture that prevented freezing.
This summarizes the core argument of Scientist 2.
3
Evaluate the answer options against the identified claim of Scientist 2.
The option stating that methane produced by early microbes, alongside moderate carbon dioxide, was the primary greenhouse gas mixture aligns perfectly with Scientist 2's argument.
This confirms the correct choice while eliminating the distractors representing the other scientists' views.

Key Concept

Identifying Core Claims and Hypotheses
Estimated Time:1m 30s
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Topics

Identifying Core Claims and Hypotheses

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