Q15 - Earthworms, vital to the health

[ohthatpatrick]

What does the Question Stem tell us?
Necessary Assumption

Break down the Stimulus:
Conclusion: Putting crushed limestone on the soil's surface should make the soil more attractive to earthworms.
Evidence: The top layer of soil can get highly acidic. Earthworms prefer soil that is neutral on the acid-to-alkaline scale. Crushed limestone is highly alkaline.

Any prephrase?
The author assumes that the crushed limestone will get overly acidic soil back to the neutral level that earthworms like. Any potential objections with this plan? What if there weren't plants decomposing and the soil was neutral? Wouldn't the limestone make the soil too alkaline? What if the soil IS acidic but the limestone goes overboard and brings the soil too far into alkaline territory? What if there's some other attribute of limestone that is detrimental to earthworms or to something earthworms otherwise care about?

Correct answer:
B

Answer choice analysis:
A) Red flag: "most" important function? Not to mention, we never even said or implied that earthworms perform this function.

B) This works. This is just stating the author's intention: the limestone will bring the soil from overly acidic back to neutral. If we negate this, it's a huge objection "The limestone doesn't stay in the soil long enough to neutralize any of the acidity".

C) Red flag: "just as vital"? Also, we never talked about Ca or Mg. This is a good example of an answer that Strengthens, but is not Necessary.

D) Red flag: "does NOTHING"? Why would the author care if acidity somewhat hastened plant decomposition? And what does this have to do with the conclusion, which is about the possible effects of limestone?

E) Red flag" SIGNIFICANTLY more likely". This argument doesn't care whether the soil gets any benefit from the earthworms. It cares whether the soil is attractive TO earthworms.

Takeaway/Pattern: The author has a PLAN to achieve a DESIRED RESULT. The correct answer states something that would have to be true, at a minimum, to believe that this plan might actually work. If we negated the correct answer, it would definitively tell us that the plan will NOT work.

#officialexplanation

[lsatgotrocked]

I just want to put out my thoughts on this q, so that others could refer to it if they need help.

We must first note that this is a necessary assumption question. The process to solve these types of questions first begins with identifying the argument core.

The conclusion: Application of crushed limestone to the soil surface makes the soil more attractive to the earthworms.

Premises: The decomposition of the dead plants makes the top layer of soil highly acidic, and acidic soil is not as preferable to worms when compared with neutral soil.

Now we identify the gaps. Remember to be flexible. These questions tend to offer a nice prephrase, but sometimes the answer won't be one that you were initially expecting.

The gap that initially jumped out at me during my timed practice test was one regarding duration of effectiveness. The author says that it will help make the soil more attractive (i.e. it will make it less acidic - this is what alkaline means, a pH greater than 7). What if the soil is only made less acidic immediately after the crushed limestone is applied to the soil, but then quicjly disappears allowing the soil to regain its acidity? The author MUST be assuming that the crushed alkaline will remain in the soil's top layer long enough to achieve its desired effect. This is what B is saying. Note that if we negate it - "After the application the crushed limestone does not stay in the soil long enough to neutralize the soil", the entire argument gets destroyed.

As for the incorrect answers:

A.) Irrelevant. The logic of the core is not really focusing on the function of earthworms although it does mention that they are vital to the health of the soil. We need an answer that discusses crushed limestone and its ability to neutralize the soil altogether.

C.) If this were a question that was arguing for the use of crushed limestone because of its beneficial aspects, then this could arguably be a nice answer for a strengthen question. This is a necessary assumption question. Know your task! Furthermore, if we negate this the argument is not weakened one bit.

D.) The decomposition of dead plants is, in my opinion, out of scope to this argument as a whole. If negated the argument still stands.

E.) This could be tempting to some, but is nonetheless irrelevant. The author's argument does not depend on assuming which type of soil is more likely to benefit. The argument revolves around crushed limestone and its ability to make soil more attractive to earthworms. If we negate this the logic of the argument still holds.

Hope it helps. Been studying for countless hours and wanted to give back to this great forum.