In early 2003, scientists detected methane in the atmosphere of Mars. Methane is a fragile compound that falls apart when hit by the ultraviolet radiation in sunlight. So any methane in the Martian atmosphere must have been released into the atmosphere relatively recently.
The argument relies on the assumption that
(A) Mars had no methane in its atmosphere prior to 2003
(B) all methane in the Martian atmosphere is eventually exposed to sunlight
(C) methane cannot be detected until it has started to fall apart
(D) the methane that the scientists detected had been exposed to ultraviolet radiation
(E) methane in Earth’s atmosphere does not fall apart as a result of exposure to ultraviolet radiation
A. The history of methane on Mars isn’t the issue. The argument focuses on whether methane currently exists in the upper atmosphere.
B. Correct. This is crucial to the argument. If it’s false—i.e., if some methane in the upper atmosphere is never exposed to UV radiation—then methane could persist, weakening the author’s conclusion.
C. This answer just strings together familiar terms—“methane,” “detected,” and “falls apart”—without making a meaningful connection. The argument never links the act of detection to methane disintegration.
D. The argument assumes that the detected methane hadn’t been exposed yet. That’s why it still exists. Once it is exposed, the claim is that it will break down.
E. The comparison to Earth is irrelevant. Conditions on Earth don’t affect what happens on Mars, so this doesn’t help or hurt the argument.
