Q19 - Professor Robinson: A large

[catialuong]

PT 22, S2, Q 19

" Professor Robinson: A large meteorite..."

Can someone please help me with this question?

My understanding of the argument is that there are 2 theories as to what caused mass extinction. First theory is that the meteorite impact did.
However second theory is that re-crystallized rock recovered from the site indicates the polarity is normal, but it is a known fact that polarity of earth at time of impact of meteorite was reversed polarity. So the argument is implying (never explicitly states this) that another event (not meteorite) caused the rocks to melt and re-crystallized. Thus it implies another event caused the mass extinction, NOT the impact of the meteorite. Is this understanding correct?

The answer choice presents us with 4 necessary assumptions and one that is NOT. WE need to find that one that is not. Can we assume that one correct answer is a sufficient assumption or not an assumption at all?

Can someone please explain why A is the correct answer? Wouldn’t this assumption have to hold in order for the theory that the meteorite caused the mass extinction to be true? Very muddy to me.

Thank you.

[skapur777]

Assumption A oversteps its' bounds a little bit.

A says that the crater indicates an impact of MORE THAN SUFFICIENT size to have caused the mass extinction. I eliminated because the crater does not need to be more than sufficient size.

And thus I picked this one. The other ones are necessary assumptions.

Just to further prod the moderators here, would it make any difference at all if the answer choice said that the "Crater indicates an impact of sufficient size to have caused the mass extinction"? In other words, would the answer choice still be correct?

[giladedelman]

Thanks for posting!

And thanks especially for explaining your reasoning. In fact, you're not quite catching the logic of the argument.

You're right that the conclusion is that the meteorite did not cause the extinction: "the impact that formed this crater was not the culprit." This conclusion is based on the fact that the recrystallized rocks at the site of the crater don't display the polarity that was in place at the time of the extinction.

Notice that the argument is NOT implying that the meteorite didn't cause the recrystallization; in fact, it's assuming that it did! Because of what we observed from the recrystallization, the argument implies, we know that the meteor didn't strike at the time when the extinction occurred. Therefore, it didn't cause the extinction. The other big assumption is that if the meteor did cause the melting, that the melting and recrystallization happened right away.


So (B) is necessary, because what if the rocks stayed molten for a long time, until the polarity shifted, and then recrystallized? Then the meteor may in fact have struck at the time of the extinction.

(C) is necessary because the argument is assuming that it was the impact that caused the melting. But maybe the meteor hit, and then something different caused the melting a million years later!

(D) is basically the same as (C).

(E) is another one of those "time" assumptions: the argument assumes that if something causes an extinction, it has to happen right away. But maybe the meteor hit, and then it took a thousand years for the extinction to occur as a result? (Perhaps through climate change, or something.)

So that leaves us with (A): The crater indicates an impact of more than sufficient size to have caused the mass extinction.

Guys, remember what we're trying to do here! This argument concludes that the meteor DID NOT CAUSE THE EXTINCTION! Did not. This is an assumption that supports the idea that the meteorite did cause it. It's supporting the exact opposite argument!

Dig?

[anthony.spitzer55]

Just curious how you know that the argument is implying that the meteorite caused the recrystallization?

[theanswer21324]

I've got a question about (B) if anyone is still responding to this particular thread. Is B really a necessary assumption question? For it to be necessary, I would have thought that it would need to say something along the lines of: "The recovered rocks recyrstallized sometime before the magnetic field reversed." (B) as it is characterized strikes me more as a sufficient, not necessary, assumption. Is this the wrong way of looking at it?

Thanks for your help.

[WaltGrace1983]

I've got a question about (B) if anyone is still responding to this particular thread. Is B really a necessary assumption question? For it to be necessary, I would have thought that it would need to say something along the lines of: "The recovered rocks recyrstallized sometime before the magnetic field reversed." (B) as it is characterized strikes me more as a sufficient, not necessary, assumption. Is this the wrong way of looking at it?

Thanks for your help.

I think you are probably getting at the idea of what "shortly" really means. The word is vague, but I don't think it requires too much thought. I don't think "shortly" could ever break an answer choice, though I could be wrong.

As for your hypothetical answer (B), I don't think that would really be necessary. This is because it wouldn't really do much to the argument: the author is just assuming a relationship between time of impact and time of recrystallization.

In other words, the author is assuming that the meteorite crystallized (aka, solidified its polarity so to speak) shortly after it impacted the Earth. If this were NOT to be the case, then why bring up "evidence" about magnetic polarity?

Let's examine your hypothetical (B): "The recovered rocks recyrstallized sometime before the magnetic field reversed."

The thing about this is that it doesn't tell us anything about the impact. Notice how every single necessary assumption (aka, the wrong answers) all have something about impact. In the case of (B), impact is implied as the meteorite strikes the Earth as somewhat of a fireball of molten rock.

Also, why does it have to be BEFORE the magnetic field reversed? Couldn't it be after?

Just curious how you know that the argument is implying that the meteorite caused the recrystallization?

I think that this is the essential point of the question. The author doesn't KNOW; the author ASSUMES.

What if there was SOMETHING else that caused the recrystallization (like C and D say)?

What if the recrystallization did not occur alongside the impact? (like B and E state)?

[WaltGrace1983]

I just wanted to add that, even if (A) was "sufficient size" or "less than sufficient size" or "more than sufficient size," I don't think any of it would matter.

The author is assuming that the impact was "not the culprit" of the extinction. Thus, the author could just as validly be assuming that the crater could have been more/less/just right size.

(A) would be a sufficient assumption for an OPPOSING argument I believe, something saying that the impact DID cause the extinction. However, (A) would not be a necessary assumption for such an argument.

[maria487]

I'm curious as to whether the "more than" in answer choice A is what makes that answer correct. If you remove the "more than", and the answer reads that the crater indicates an impact of sufficient size to have caused the mass extinction, would that be considered a necessary assumption? Because isn't the argument assuming that it's the crystallization which rules out the meteorite as the cause of the mass extinction? In order words, is it safe to assume that the meteorite meets the size criteria for causing the mass extinction, but fails the crystallization criteria? Or would that be too much of a stretch?

[maryadkins]

In order words, is it safe to assume that the meteorite meets the size criteria for causing the mass extinction, but fails the crystallization criteria? Or would that be too much of a stretch?

Too much of a stretch, for sure.

The argument is anti-meteorite causing extinction due to the polarity. It says nothing about size. And (A) is in favor of why a meteorite could have been the cause. This means it is inherently COUNTER to the argument, as Gilad noted, so it can never be an assumption the argument (against it!) is making. And to answer your question more specifically, saying one thing is evidence definitely does not mean implying that one thing is NOT evidence.

[maria487]

In order words, is it safe to assume that the meteorite meets the size criteria for causing the mass extinction, but fails the crystallization criteria? Or would that be too much of a stretch?

Too much of a stretch, for sure.

The argument is anti-meteorite causing extinction due to the polarity. It says nothing about size. And (A) is in favor of why a meteorite could have been the cause. This means it is inherently COUNTER to the argument, as Gilad noted, so it can never be an assumption the argument (against it!) is making. And to answer your question more specifically, saying one thing is evidence definitely does not mean implying that one thing is NOT evidence.

Hm, interesting. Thank you for your reply. I wanted to test the limits of what would be considered a necessary assumption.

Also on that note, for answer choice (E) to be a necessary assumption, are we assuming that the change in earth's polarity did not occur sometime very soon after the time when the meteorite hit? I ask because I don't see any other indication of time other than the change in earth's polarity. If I'm understanding correctly, we know that the cause of mass extinction was not the meteorite, based on the rocks' crystallization. So, in my mind, for (E) to be correct, we need to assume that it wasn't meteorite/change of earth's polarity/mass extinction is immediate succession. Am I on the right path?

[maryadkins]

It sounds like it but I'm not entirely following you. If your reasoning matches up with Gilad's, above, on (E), you're correct. He gets into timing and what's assumed here.