#19 - Professor Robinson: A large meteorite impact crater in

[James Finch]

Hi Coffeehouse,

The conclusion in the stimulus is that the large meteorite crater is not a clue to explaining the mass extinction of plant and animal species that occurred at the end of the Mesozoic era. He cites the polarity of crystallized rocks at the impact site as evidence for this. We are then asked to find which of the answer choices is not assumed by Professor Robinson, meaning which answer choice is either irrelevant to or evidence against his argument that the polarity of the rocks means that the meteorite impact doesn't tell us anything about the Mesozoic era extinction.

Remember that Robinson is trying to show that the crater is not involved with the extinction, so anything making the meteorite more likely to be a cause of the extinction should be immediately suspect. Answer choice (A) is irrelevant to Robinson's argument, because his argument relies upon other evidence (rock polarity) to make his case; imagine if he had said "Besides, the crater's size doesn't show a large enough impact to cause the extinction" at the end of the stimulus.

We can test this answer choice using the Assumption Negation technique and see that it doesn't follow:

"Since the crater does not indicate an impact of more than sufficient size to have caused the mass extinction, the crater is a clue to explaining the mass extinction."

The "more than" does leave room for ambiguity as to whether it could be a clue to the extinction, but does not work in definitively falsifying Robinson's conclusion. This means it cannot be an assumption depended upon by the argument.

[menkenj]

I interpreted answer choice A to mean "At the very least, the crater's size crosses the threshold sufficient to have caused mass extinction." I understand now that the answer choice refers to being greater than the sufficient threshold to cause the extinction. I guess I read "more than sufficient" to mean "crosses the threshold or barrier of sufficiency;" in other words, "AT THE VERY LEAST sufficient, possibly greater."

Am I correct in understanding that had answer choice A said "The crater indicated an impact AT THE VERY LEAST sufficient, possibly greater, to have caused the extinction" then that would be an assumption of the argument?

I actually came here to write that the psyshometricians played on the commonly used phrase "more than sufficient" to trick us. In everyday use, I often hear this phrase being used to mean there is plenty, enough. But in the LSAT sense, "more than sufficient" goes further than the everyday use of the phrase. And in this answer choice, it goes too far.

[menkenj]

For clarification, in everyday use people often say, there is "more than enough" to mean "we are good, there is enough."
But in LSAT terms more than enough/sufficient does not mean enough. It goes further and literally means MORE than enough.

Not sure if this will resonate with everyone but I fell for this trap and I think my above explanation is why.

[cornflakes]

Hi,

I was a bit tripped up between A and E and fortunately ended up selecting the right answer - I found that A seemed to strengthen the point that the author was actually arguing against. Because the I found the content very dense, I had to dumb it down a little.

Basically there is a view that a crater that was caused by a meteor can serve as way of explaining the mass extinction of animals/plants at the end of the M era. The author is arguing against this view by discussing the discrepancies of the crystalline structures of the rocks at the site (the evidence against the view). The author claims that crystallized rocks display polarity (could be any characteristic) that is consistent with the period in time that they crystallize - essentially, this characteristic is frozen in time and does not change. The author then says that because these crystallized rocks display polarity (again, any characteristic, but something that is shown to be frozen in time once established) that is inconsistent with the polarity (characteristic) on earth at the time the crater was formed.

To me, B, C, and D can be quickly eliminated because they all strengthen the connection concerning the research methods - using the rock's crystalline structure as an accurate dating mechanism - by negating possibilities that would weaken this connection. That narrowed things down to A and E. The negation of E - the mass extinction would not have occurred soon after the impact that supposedly caused it - would weaken the argument because it weakens the viability of using the premises to prove the conclusion. It allows for a greater chance that the polarities of the earth would actually be different at the time of extinction versus at the time of crater impact.

But I don't even think this level of analysis is necessary here considering how blatantly wrong A is. Why would the author, who is arguing against the idea that the crater can help explain the extinction, need to assume that the impact was more than large enough to cause the mass extinction? This information alone would actually weaken their view and strengthen the view that they are trying to argue against. Thus, this was the real time reason I chose A.

[Ryan Twomey]

Hey I comletely agree with your statement, "But I don't even think this level of analysis is necessary here considering how blatantly wrong A is."

A ends up being the correct answer because it is an "except question" but in a normal assumption question this would be blatantly wrong as you said. In some questions it is better to do process of elimination and some questions it is better just to pick an obviously correct answer, in this case A is blatantly correct.

This is because our conclusion is essentially: 'it was not the meteor that caused the extinction.' When A is negated it actually strengthens our conclusion, making it impossible to be an assumption necessary. Which in this case makes it the correct answer. All you needed to do to get this question correct is understand the conclusion and negate answer choice A. This could be a quick process.

Sometimes the LSAT gives you an overly dense stimulus and then gives you an easy answer choice. Let the answer choice be easy. Use your conclusion to help you out in an overly dense stimulus.

I hope this helps. I think you thought through this well but I just thought I would reinforce your idea that A is blatantly correct here and remind you not to overanalyze this overly dense and complicated stimulus when all you really need to understand is the conclusion.

Best,
Ryan

[Amrita22]

Hi Powerscore Team,

I hope you are well. I am curious why the argument relies on Answer Choice C: Suppose that another event, at the exact same time as the impact, melted the rocks (implausible, I know). Then, wouldn't Professor Robinson's argument still be good, because the crystallization of the polarity could still be indicative that the impact was not the cause of the extinction? I realize that answer choice A is the BEST answer. Any clarity you can provide would be much appreciated. Thank you.

[Adam Tyson]

Let's explore the negation of answer C, Amrita22. If some other event caused the rocks to melt after the crater was formed, there would no longer be sufficient reason to believe that the impact did not cause the extinctions. Maybe it did, maybe it did not, but the evidence about the magnetic polarity in those recrystallized rocks would no longer be very persuasive, would it? The meteor could have caused the extinctions and then, sometime later, after the Earth's polarity had changed, something else could have melted the rocks and they could have recrystallized with the new polarity!

An assumption is necessary not because it proves the argument is correct, but rather because the argument loses its logical force without it. For that reason, the negation - saying the answer is not true - doesn't have to disprove the conclusion, but merely take away the force of the evidence such that the conclusion loses all support.

[ltowns1]

So recrystallization involves a melting process.. When I realized that it made the problem much easier, isn’t that kinda straddling the line of “common knowledge”?

[Adam Tyson]

Not at all, ltowns1! That information is already in the stimulus, when they said "When molten rocks crystallize...". They've already indicated to us that melting precedes recrystallizing, and in the process have implied that the rocks at the meteor impact site had, at some point, melted (presumably as a result of the meteor impact, which is one of the underlying assumptions found in the answer choices).

[ltowns1]

Gotcha! Thank you!