Soru

### The Origin of Earth's Water

How Earth acquired its vast oceans is a subject of ongoing debate among geochemists and planetary scientists. Two models have been proposed to explain the origin of Earth's water.

Model 1
During Earth's formation, the high temperatures of the inner Solar System caused volatile compounds, including water, to evaporate. Consequently, the proto-Earth accreted as a dry body. Approximately 3.9 billion years ago, during the Late Heavy Bombardment, a "late veneer" of carbonaceous chondrite asteroids and comets from the outer Solar System collided with Earth. These impactors were rich in water and other volatile compounds, depositing the water that eventually formed the oceans. The deuterium-to-hydrogen ($D/H$) ratio of Earth's current oceans matches that of carbonaceous chondrite asteroids, supporting this external origin.

Model 2
Earth's water was present from the beginning of its accretion. Water-bearing minerals, such as ringwoodite, were part of the rocky material that formed the proto-Earth. As Earth underwent differentiation into core, mantle, and crust, heat from radioactive decay and gravitational collapse caused these hydrous minerals to release water vapor. This water vapor was transported to the surface through volcanic degassing, eventually condensing to form the oceans. This model argues that the $D/H$ ratio of Earth's oceans reflects the isotopic composition of the early solar nebula, rather than later external delivery.

According to the passage, Model 1 and Model 2 differ in which of the following ways regarding the state of the proto-Earth during its accretion?