**Text 1** For decades, planetary scientists have maintained that the bulk of Earth’s wate… — SAT

Text 1
For decades, planetary scientists have maintained that the bulk of Earth’s water was delivered by carbonaceous chondrites during the late accretion phase of planetary formation. Proponents of this model point to the deuterium-to-hydrogen ( $D/H$ ) ratios of these water-rich meteorites, which are virtually identical to the isotopic signature observed in Earth's modern surface oceans, suggesting a post-formation meteoritic origin.

Text 2
Geochemist Wu and colleagues propose that a substantial fraction of Earth's water instead originated from the primordial solar nebula. The team analyzed deep-mantle rock samples, which yield a significantly lower $D/H$ ratio than that of surface reservoirs. Wu argues this low ratio reflects nebular hydrogen directly absorbed by the early magma ocean, meaning modern ocean values represent a hybrid mixture rather than a purely chondritic source.

Based on the passages, is the statement that geochemist Wu and colleagues would characterize the isotopic match described in Text 1 as insufficient evidence to establish that Earth's water was delivered entirely after the planet's initial formation true or false?

Answer: Answer

Answer

True

The statement is true because the author of Text 2 introduces evidence of a solar nebula origin (low

D/H

ratios in the mantle) to argue that modern oceans are a hybrid mixture. This directly implies that the isotopic similarity between surface oceans and chondrites cited in Text 1 is insufficient to prove that all of Earth's water arrived post-formation.

Step-by-Step Solution

Analyze Text 1's claim and evidence.

Text 1 claims that the bulk of Earth's water was delivered post-formation by carbonaceous chondrites, citing the identical deuterium-to-hydrogen (

D/H

) ratios between these meteorites and modern surface oceans as primary evidence.

To understand the baseline argument that Text 2 is responding to.

Analyze Text 2's counter-evidence and claim.

Text 2 introduces geochemist Wu's findings that deep-mantle rocks have lower

D/H

ratios, suggesting hydrogen was absorbed from the solar nebula during the early magma ocean phase (during planetary formation).

To identify the alternative source and mechanism proposed for Earth's water.

Synthesize the relationship between the two perspectives.

Wu does not discount chondrites but argues that modern oceans represent a hybrid mixture of nebular and chondritic water. This implies the surface ocean

D/H

ratio alone is not sufficient to conclude that all of Earth's water was delivered post-formation.

To determine how the author of Text 2 characterizes the scope and validity of Text 1's evidence.

Evaluate the true/false statement.

Since Wu's argument directly shows that surface ocean ratios do not tell the whole story (representing a hybrid rather than pure chondritic source), he would indeed view the isotopic match as insufficient to establish a purely post-formation origin. The statement is therefore True.

To arrive at the final logical conclusion.

Key Concept

Cross-Text Connections: Relational Synthesis

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