#7 - Two different dates have been offered as the

[lilmissunshine]

Hello,

I can see why (E) is correct but I was wondering why (D) is inferior. Is it because (D) does not summarize the stimulus as thoroughly as (E), although the answer choice itself is supported by the evidence?

Many thanks!

[Alex Bodaken]

lilmissunshine,

Thanks for the question! The problem with answer choice (D) is that it assumes a bit too much given what we have in the stimulus. Specifically, all the stimulus tells us is that one of the dates for the end of the ice age was found by seeing "when warmth-adapted open-ground beetles replaced cold-adapted arctic beetles." But answer choice (D) posits that "The species of cold-adapted arctic beetle that inhabited areas covered by ice masses died out toward the end of the last ice age." It's the "died out" that is the issue here - we don't know that they died out. They could have, for instance, just moved to a different layer of sediment, or migrated to another place. The phrase "died out" is sufficient to make answer choice (D) incorrect, which leaves answer choice (E) credited.

Hope that helps!
Alex

[sunshine123]

Okay, I see how E, if we assume that it is saying that warmth-adapted beetles came before spruce forests, is correct. After all, that's what it says in the stimulus. However, E seems to be saying much more than that. In the first place, the answer states that the beetles "colonized NEW terrain" faster than the spruce trees. The stimulus never mentions that the warmth-adapted beetles replaced cold-adapted beetles in response to changes in terrain. Maybe the terrain was the same, and what pushed the replacement of beetles was simply a change in temperature. If that were the case, then it wouldn't really make sense to speak of warmth-adapted beetles "colonizing new terrain faster than the trees, " unless we assume the changes in terrain had already been in place at the time warmth-adapted beetles took over, as answer choice E assumes. Are my suspicions warranted?

Thanks!

[Adam Tyson]

Think of colonizing new terrain as new to THEM, sunshine123. If the warmth-adapted beetles were replacing the cold-adapted ones, then they were taking over land that they had not currently held.

Think of any historic colonization among humans. The land being colonized wasn't new land - the land already existed and there were some people there already in most cases - but it was new land from the perspective of the colonizers.

The prephrase here should be along the lines of "the beetles changed before the land changed," and that is exactly what answer E is saying. As the ice age ended, the warmth-adapted beetles took over from the cold ones 500 years before the spruce forests took over from the ice masses.

[CJ12345:]

Hi, Powerscore
Since this question is asking us to find the conclusion, I am not sure why C is not the correct AC. C, like E, also gives an explanation in terms of why the replacement of beetle is 500 yrs earlier than the replacement of spruce forests to the ice masses. C gives an explanation by the statement that ice masses continued to advance (replacement of spruce took place later) after the end of the ice age (beetle replacement occurs).

[Luke Haqq]

Hi CJ12345:!

From my understanding of your issue, it seems like you might be inserting content into answer choice (C) that isn't actually in that answer choice. In particular, I wasn't sure that I understood how the parenthetical information you included was necessarily was implied from the language of the answer choice. Do feel free to elaborate if you can. As I read the answer choice, it doesn't give us any definite information about beetles and trees--indeed, beetles and trees are not mentioned anywhere in the answer choice.

Ultimately, we don't know whether or not ice masses continued to advance through North America for several hundred years after the last ice age. Ice masses are mentioned in the stimulus--we're told that they "yielded to" spruce forests. But we don't know whether or not these ice masses continued to exist after this, nor do we know how long they might have continued to existed. Since we don't know more about how long ice masses might have continued to exist after the last ice age, we can't know (C) to be true based off of the stimulus.

[jimmy1115]

Hi,

I am trying to confirm if my understanding of why (C) is incorrect is right.

I originally picked (C) because I thought the replacement of beetles (first date) indicates the end of the last ice age, thus having it occurred 500 years earlier than the second date means that ice masses continue to advance for several years (500years) after the end of the ice age (indicated by first date- beetle replacement).

Is (C) incorrect because we do not know which date indicates the end of the ice age? i.e. the first dates- when warmth-adapted beetles took over cold ones, we don't know for sure this is the time when the ice age ends right? Because otherwise if the first date IS the end of the ice age, then (C) should be correct.

Thank you

Best,
Jimmy

[Adam Tyson]

My thought about answer C was just this, Jimmy: we have no information at all about ice masses advancing. None. We can tell that the ice masses had not yet yielded to spruce forests when the warmth-adapted ground beetles replaced cold-adapted ones, but were the ice masses advancing, receding, or standing still?

Digging a little deeper into that answer, we find another problem: the whole point of the investigation was to determine when the ice age ended. The facts never established that date. Was it when the beetles changed, or when the forests took over? We don't know! So how can we infer that the ice masses were even still around when the ice age ended, let alone whether they were advancing? That would require us to decide that the earlier date was the correct one, AND to assume that the ice masses were advancing during the next few hundred years before the spruce forests took over. That answer needs way too much help for it to be a valid inference; the correct answer should need no help at all, because the facts in the stimulus would support it all by themselves.