#13 - In early 2003, scientists detected methane in the

[chris12]

Hi, I chose D because it made the most sense, but I still don't think that the argument needs to assume D to be true. We know that sunlight makes methane fall apart, but there is still the possibility that other things make methane fall apart. So, the argument doesn't need to assume that methane is exposed to sunlight, but rather anything that makes it fall apart.

[KelseyWoods]

Hi Chris!

First, I just want to clarify that the correct answer to this question is answer choice (B): "all methane in the Martian atmosphere is eventually exposed to sunlight."

You're right that if we just focus on the conclusion out of context, it seems like the assumption of the argument is that any methane in the atmosphere would soon be exposed to anything that would cause it to fall apart. But we need to look at the overall context of the argument, not just the conclusion. We're looking for something that the author assumed in jumping from that premise to that conclusion. The author thinks the methane detected in the atmosphere of Mars must have been released relatively recently. Why? Because methane falls apart in sunlight. What must the author be assuming if they think that the fact that methane falls apart in sunlight means that the detected methane must have been released recently? The author is assuming that all of the methane in the atmosphere is eventually exposed to sunlight. Sure, there may be other things that cause methane to fall apart. But if the author is drawing that conclusion from the premise that methane falls apart specifically when exposed to sunlight, that means that the author is assuming that all of the methane in the atmosphere will eventually be exposed to sunlight.

So remember that we're looking for something necessary to the argument as a whole. Often, we can just focus on the conclusion to do this. But we can't ignore the broader context of the premises. Ultimately, an assumption is something the author assumes in jumping from the premises to the conclusion so the relationship between them is important!

Hope this helps!

Best,
Kelsey

[bluebell]

This one really troubles me because I was pretty certain that D was a necessary assumption because I understood it as saying that the methane discovered by the scientists had been exposed to UV AFTER having been discovered and therefore fell apart making the new methane recent.
Please help.

[Beth Hayden]

Hi Blue,

The stimulus just says that at some point in 2003 scientists found methane in the Mars atmosphere--we don't have any idea what happened after that, we just know that at this particular moment in time methane was found. Then the stimulus argues that because methane will fall apart when it encounters sunlight, the methane they found must have been released recently, otherwise it would have fallen apart already.

Imagine you walk outside on a warm sunny day and see snow on the ground. You would probably assume that it snowed really recently, because otherwise the snow would have already melted. That's the reasoning that the author uses in the stimulus. Now, that argument makes a lot of sense on a hot sunny day, but it doesn't make much sense when it's freezing cold in Alaska in the dead of winter. In that case, the snow could have fallen yesterday or it could have fallen months ago.

That's what answer choice (B) is getting at--in order for this reasoning to make sense we have to assume that the methane was going to get exposed to sunlight eventually. If it was found somewhere on Mars that is never exposed to the sun, like in a dark cave for example, who knows how old it is!

Answer choice (D) says that for the argument to be true we would have to assume that the methane they found had already been exposed to ultraviolet radiation. But that's not necessarily true. Maybe the scientists went to an area of the planet where it was nighttime and the methane had just been released, so it hadn't yet seen sunlight but would soon? The argument would still work. However, the argument definitely falls apart if the methane was found in an area that never sees sunlight at all.

Hope that helps!
Beth