PT11.S3.Q15 (P3) - Amazon Rain Forest Species Diversity #Help

Maxwell-1

I am working through drilling RC sections and PT11 S3 Q15 has me stumped.

The question asks for the assumption which the argument relies on, which means that the assumption shouldn't be stated.

I narrowed the choices down to (A) and (C).

I ultimately chose (A) because I found (C) explicitly stated in the passage (See lines 6-10 + 15-18, line 6-10 states that the only way for species growth in the manner that occurred in the deep sea mud is for there to not have been significant changes in climate, and then starting at line 15 he states that the amazon didn't have significant changes in climate. )

I don't see how a question can ask for an assumption the argument relies on, which I read as a Necessary Assumption then have the answer be a premise stated, not assumed.

Can someone help me bridge the gap here? I am clearly missing something.

Help

Admin Note: https://7sage.com/lsat_explanations/lsat-11-section-3-passage-3-questions/

Ashley2018-1

So the author starts off by making a comparison between Amazon River Basin and the deep sea but these are two vastly different environments at first glance, so what makes the author think he can make such a comparison? He tells us from the start, that it's the climactic stability, or "the absence of signifiant fluctuations in climate and physical conditions" that makes these two places comparable. But if this node of comparison were untrue (if answer choice C were negated), then the author shouldn't be able to draw such a comparison at all, and that is what answer choice is getting at.

I think A is factually true, meaning that you can support it from lines in the passage but the question is getting at the basis of this claim. Why is it so that the Amazon and deep sea share this similarity? Because both are climatically stable.

Toolinshed

Actually, you have it the other way around. The rate of speciation is something that was stated to be true, not an assumption. "The old belief that climate stability accounts for high level of species diversity." If something is accounting for it, it's probably the case that it's already true or at least believed to be true.

As for C, the passage uses the deep sea as an comparison to the Amazon basin, by assuming that both haven't had any drastic changes take place. Later on in the passage however, it is clarified that they actually aren't the same. He never explicitly claims that is was. The passage also uses words like "could be" (line 7) which further solidifies that this is an assumption.