Two students discuss the origin of water on Earth. **Student 1** Earth's water was deliver… — ACT

Two students discuss the origin of water on Earth.

Student 1
Earth's water was delivered primarily by icy comets that collided with Earth during its early history. Comets contain water ice with a high deuterium-to-hydrogen ( $D/H$ ) ratio. If comets were the primary source, the $D/H$ ratio of Earth's oceans must be equal to the $D/H$ ratio found in comets.

Student 2
Earth's water originated from volcanic outgassing of water vapor from the mantle. Hydrated minerals deep within the Earth were heated, releasing water that eventually formed the oceans. Since mantle water has a much lower $D/H$ ratio than comet water, the $D/H$ ratio of Earth's oceans must be lower than the $D/H$ ratio of comets.

Match each statement regarding the origin or properties of Earth's water to the student whose viewpoint it represents.

Earth's water came from volcanic outgassing of the mantle.Supported by Student 2's explanation of water origin
Earth's water came from comet collisions during early history.Supported by Student 1's explanation of water origin
The $D/H$ ratio of Earth's oceans is lower than that of comets.Predicted by Student 2's explanation of ocean chemistry

Answer

The statement about volcanic outgassing matches Student 2's water origin theory; the statement about comet collisions matches Student 1's water origin theory; and the prediction that the ocean's D/H ratio is lower than that of comets matches Student 2's chemistry prediction.

The correct matches align with the specific claims made by each student. Volcanic outgassing is Student 2's proposed source, comet collisions is Student 1's proposed source, and the lower D/H ratio is Student 2's prediction.

Step-by-Step Solution

Analyze Student 1's viewpoint.

Student 1 claims that Earth's water came from comets and that the ocean's D/H ratio should equal that of comets.

This establishes which items belong to Student 1's argument.

Analyze Student 2's viewpoint.

Student 2 claims that Earth's water came from mantle outgassing and that the ocean's D/H ratio should be lower than that of comets.

This establishes which items belong to Student 2's argument.

Perform the matching based on these claims.

Volcanic outgassing matches Student 2's origin; comet collisions matches Student 1's origin; the lower D/H ratio matches Student 2's prediction.

This completes the correct matches.

Key Concept

Identifying points of disagreement between different scientific viewpoints based on their premises and predictions.

Estimated Time:1m 0s

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