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Difficulty: MediumIdentifying Core Claims and Hypotheses

### Origin of the Earth's Moon

The Earth's Moon is unusually large relative to its parent planet and has a low bulk density compared to Earth, indicating that it lacks a large metallic iron core. Two hypotheses have been proposed to explain the origin and composition of the Moon.

Hypothesis 1
The Moon formed when a Mars-sized protoplanet collided with the newly formed Earth early in the history of the solar system. The extreme heat generated by this impact vaporized the outer rocky mantles of both bodies, ejecting a disk of silicate debris into orbit around the Earth. The metal core of the impacting body sank and merged with the Earth's core. Over time, the iron-depleted debris in orbit accreted to form the Moon, explaining its small core and low density.

Hypothesis 2
The Moon and Earth formed simultaneously from the same local cloud of gas and dust in the early solar nebula. As dust particles collided and adhered, two separate gravitational centers grew adjacent to each other. The difference in density and iron content is explained by a process where the heavier iron particles gravitated toward the center of the larger Earth-forming mass before the final accretion of the Moon began, leaving the remaining cloud iron-depleted.

Based on the passage, according to Hypothesis 2, what is the primary cause of the Moon's lower density compared to Earth?

  1. A
    Earth's stronger gravitational pull stripped the metallic iron core out of the Moon after both bodies had fully formed.
  2. B
    Debris from the rocky mantles of Earth and a colliding protoplanet coalesced in orbit after a massive collision.
  3. The heavier iron particles in the shared dust cloud migrated toward the larger Earth-forming mass prior to the Moon's accretion.Answer
  4. D
    The Moon was formed in a different region of the solar system with less iron and was subsequently captured by Earth's gravity.

Answer

The correct answer states that the heavier iron particles in the shared dust cloud migrated toward the larger Earth-forming mass prior to the Moon's accretion.
According to Hypothesis 2, the Earth and the Moon formed from the same local cloud of gas and dust. The lower density of the Moon is explained by the movement of heavier iron particles toward the larger Earth-forming mass before the Moon finished accreting, which left the remaining dust cloud depleted of iron.

Step-by-Step Solution

1
Locate the discussion of Hypothesis 2 in the passage.
Hypothesis 2 is presented in the third paragraph of the text.
The question specifically asks about the mechanism described in Hypothesis 2.
2
Find the explanation for the Moon's lower density and low iron content under Hypothesis 2.
Hypothesis 2 explains that heavier iron particles gravitated toward the center of the larger Earth-forming mass before the final accretion of the Moon began, leaving the remaining cloud iron-depleted.
This identifies the specific core claim and physical sequence proposed by Hypothesis 2.
3
Evaluate the choices to find the one matching this explanation.
The option stating that heavier iron particles in the shared dust cloud migrated toward the larger Earth-forming mass prior to the Moon's accretion matches the passage details.
This confirms the correct option.

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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