Question

Origin of the Moon

Three models are proposed to explain the origin of Earth's Moon.

Model 1 (Giant Impact)
Approximately 4.5 billion years ago, Earth collided with a Mars-sized planetesimal called Theia. The collision vaporized Earth’s outer crust and mantle, as well as Theia. The resulting debris ring orbitally coalesced to form the Moon. Because the Moon formed primarily from the vaporized silicate mantle materials of both bodies, it has a very small iron core, a low overall density compared to Earth, and an oxygen isotope ratio nearly identical to Earth's mantle. This model asserts that the extreme heat of the impact depleted volatile elements (such as water and sodium) on the Moon.

Model 2 (Co-formation)
The Earth and the Moon formed simultaneously from the same region of the solar nebula’s accretion disk. As gravity drew dust and gas together, two adjacent accretion centers developed: a larger one for Earth and a smaller one for the Moon. Because they formed from the same reservoir of material, their oxygen isotope signatures are identical. However, this model assumes that both bodies should have similarly sized iron cores and overall densities, as the starting material was uniform throughout that region of the disk.

Model 3 (Capture)
The Moon formed in a different region of the solar system, rich in silicates but poor in iron, explaining its low density and small iron core. Later, as the Moon traveled through the inner solar system, Earth’s gravitational field captured it into a permanent orbit. Because the Moon formed in a separate region of the solar nebula, its initial composition—including its oxygen isotope ratios—was distinct from Earth's. The capture mechanism required a thick primeval atmosphere or tidal dissipation to slow the Moon down during its close flyby.

Based on the passage, which of the following statements correctly identifies a point of disagreement between Model 2 and Model 3 regarding the Moon's formation, and the resulting prediction of its oxygen isotope ratios?