Soru

Passage A
For decades, mainstream planetary geochemists held that Earth formed as an essentially dry protoplanet in the inner solar system. Under standard models of planetary accretion, the intense thermal conditions near the nascent Sun would have volatilized light compounds, driving off water vapor and preventing hydrous minerals from incorporating into the building blocks of the inner planets. Consequently, researchers concluded that Earth’s vast hydrosphere must have been supplied exogenously after the planet’s primary accretion phase was complete. This prevailing "late veneer" model posits that Earth acquired its water, organic compounds, and precious volatile elements through a prolonged bombardment of carbonaceous asteroids and icy comets originating from the colder, outer regions of the solar system.

Central to this hypothesis is the analysis of isotopic geochemical fingerprints. Specifically, the ratio of deuterium to hydrogen (D/H) measured in carbonaceous chondritic meteorites closely matches the D/H ratio found in modern terrestrial oceans. Because isotopic fractionation processes are relatively predictable, proponents argued that this geochemical correspondence provides decisive proof that external impactors seeded the prebiotic Earth’s surface. From this perspective, the existence of oceans is not an inevitable consequence of terrestrial planetary formation, but rather the accidental byproduct of late-stage orbital perturbations in the outer asteroid belt that directed water-rich bodies inward.

Passage B
While the late veneer hypothesis has long dominated discussions of planetary volatiles, emerging geophysical evidence suggests that Earth’s water is predominantly endogenous. Recent high-pressure laboratory experiments and seismic imaging reveal that the mantle transition zone, situated hundreds of kilometers beneath the crust, contains minerals such as ringwoodite capable of storing several times the volume of all modern oceans within their crystalline structures. If the deep interior retains such vast quantities of water bound as hydroxyl groups in silicate lattices, the necessity of invoking external delivery mechanisms diminishes significantly.

Moreover, isotopic investigations of primitive volcanic rocks from deep-mantle plumes have identified hydrogen signatures that differ markedly from both modern seawater and carbonaceous chondrites. These ancient basalts exhibit exceptionally low deuterium-to-hydrogen ratios, pointing to an original, primordial water reservoir trapped directly from the solar nebula during the earliest stages of planetary accretion. Although late asteroidal and cometary impacts undoubtedly deposited some volatile elements onto the crust, such exogenous contributions were likely supplementary. The primary driver of ocean formation was sustained mantle degassing: as volcanic eruptions continuously transported mantle fluids to the surface throughout the Hadean and Archean eons, internal water reserves steadily accumulated to form the global hydrosphere.

Based on the passages, both authors would be most likely to agree with which one of the following statements?