PrepTest 137

Incorrect. The statement in question does have justification—that Mars escaped bombardment, so life could have formed there before Earth.

Incorrect. The statement in question does have justification—that Mars escaped bombardment, so life could have formed there before Earth.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Valid

Question Type:
Methods of Reasoning

Stimulus Summary:
Earth - Bombarded repeatedly by space rocks, so the surface was sterilized, preventing life
Mars - No bombardment, so may have had life before Earth
New fact - Many rocks from Mars ended up on Earth
Hypothesis - Life was carried from Mars to Earth

Answer Anticipation:
Didn't know you were a Martian, huh?

This Astronomer brings up a lot of information in order to bring up a hypothesis—that life may have started on Mars and then was carried to Earth on a meteorite. The entire argument is meant to show that this hypothesis isn't outlandish but fits the information we know.

What information is that? Well, Earth, unlike Mars, was bombarded by space rocks early in its history, preventing any life from forming on it. This raises the possibility that life formed on Mars during a period when it couldn't have formed on Earth. From that, it brings up the fact that many Martian meteorites ended up on Earth, presenting a mechanism by which life could have traveled from the red planet to our home. These two details build together to show that the hypothesis is plausible.

The statement in question is the first part of this argument for the hypothesis, showing that life could have formed on Mars. Structurally, it's a conclusion ("and so . . . ") that supports the main point. Any mix of these elements could come together to form the correct answer, so let's stay flexible as we analyze them.

Answer Explanation:
The statement in question is justified by the clause immediately preceding it ("and so . . . "). It's also required for the hypothesis to make sense—if life couldn't form on Mars before it did on Earth, then life on Earth couldn't have started when microbes traveled from Mars. This is our answer.

Key Takeaway:
A rare Methods of Reasoning question where the logic of the argument is important in analyzing the answers! These harder Methods of Reasoning questions frequently derive their difficulty from the way the answer choices are written, so be sure to leave yourself time to analyze them and don't spend too much on the argument itself.

Incorrect. While the statement does have justification, it isn't sufficient to establish the conclusion. While it's necessary for life to be on Mars first for the hypothesis to make sense, there being life on Mars doesn't explain—by itself—how it ended up on Earth.

Incorrect. As we explored in (C), the answer is necessary for the conclusion to hold, so this answer is incorrect.