Climatologists believe they know why Earth has undergone a : Critical Reasoning (CR)

gmat1220

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Re: Climatologists believe they know why Earth has undergone a [#permalink]

12 Mar 2011, 23:15

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I pick A.

Conclusion : Fluctuations in the earth's orbit cause the ice ages
Pros : Clouds; earth's orbit fluctuations coincide with ice ages
Cons : Clouds have to be dense

A is irrelevant to the conclusion.

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Re: Climatologists believe they know why Earth has undergone a [#permalink]

12 Mar 2011, 23:33

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Hmmm.....not every CR is that easy :-)

Think again!!

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Re: Climatologists believe they know why Earth has undergone a [#permalink]

12 Mar 2011, 23:38

Is it C bcos it did not say too dense?

vjsharma25 wrote:

Hmmm.....not every CR is that easy :-)

Think again!!

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Re: Climatologists believe they know why Earth has undergone a [#permalink]

12 Mar 2011, 23:47

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IMO C, because it bring another cause into picture other than external influence (Cosmic Dust). Volcanic activity is an internal activity, and if that becomes the root cause of periodic ice Age then cosmic theory fails to justify

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Re: Climatologists believe they know why Earth has undergone a [#permalink]

12 Mar 2011, 23:58

Guys think again. Question asks for the points that can "would lend support" to what has been stated in the argument.
(C) says Earth’s average temperature drops slightly shortly after volcanic eruptions spew large amounts of dust into Earth’s atmosphere.

So this is actually supporting the theory that due to dust(not cosmic) temperature has dropped(although slightly),leading to ice-age.

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Re: Climatologists believe they know why Earth has undergone a [#permalink]

13 Mar 2011, 00:15

E uses "rare" trace. Its the prima evidence.

It has to be D.

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Re: Climatologists believe they know why Earth has undergone a [#permalink]

14 Mar 2011, 01:32

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D is the option that does not strengthen the argument
D )Large bits of cosmic rock periodically enter
Earth’s atmosphere, raising large amounts of
dust from Earth’s surface.
Nothing has been mentioned abt the rise of dust from the earths surface and how it affects temperature on Earth.

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Re: Climatologists believe they know why Earth has undergone a [#permalink]

24 Apr 2014, 09:39

Zatarra wrote:

D is the option that does not strengthen the argument
D )Large bits of cosmic rock periodically enter
Earth’s atmosphere, raising large amounts of
dust from Earth’s surface.
Nothing has been mentioned abt the rise of dust from the earths surface and how it affects temperature on Earth.

Could someone please explain this CR? I still find it quite confusing.
Pqhai do you want to give this a try with your elegant approach?

Thanks!
Cheers
J

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Re: Climatologists believe they know why Earth has undergone a [#permalink]

30 May 2014, 15:01

Hey guys, we need OE for this one, it is still not clear to me how D is the correct answer

Prasi, you wanna give this one a try?

Cheers
J

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Re: Climatologists believe they know why Earth has undergone a [#permalink]

10 Jun 2014, 11:05

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prasi55 wrote:

Dear jlgdr,

Sure, let me try.

What is the climatologists' main hypothesis? -- Cosmic dust (resulting from the fluctuations caused during the ice age cycles) caused the ice ages.

What could support this hypothesis? Evidence of the existence of the cause (cosmic dust) or evidence that a similar cause has produced a similar effect would support it.

What could weaken this hypothesis? Evidence that things other than cosmic dust were present at that time (confounding the cosmic dust => ice age hypothesis) or evidence that unrelated things have produced a similar effect would weaken it.

A says that the clouds of dust did not appear before the regular sequence of ice ages started. If the clouds had appeared before then, then you should have expected the regular sequence of the ice ages to start before as well.

B provides evidence that the arrival of the cosmic dust coincided with the start of the regular sequence of the ice ages.

C suggests that cosmic dust has caused near-immediate drops in temperatures in the past.

E suggests that cosmic dust was likely present during the times the ice ages occurred.

Thus, A, B, C, and E do support the hypothesis (however indirectly).

What about D? D says that cosmic dust periodically enters the Earth's atmosphere. Fair enough. If D provided evidence that these periods corresponded to the occurrence of the ice ages, the hypothesis would be strengthened. But D goes on to say that the cosmic dust causes large amounts of dust from the Earth's own surface to appear.

All this dust has indeed made the picture a tad murky.

. We are no longer sure "which" dust (or whether any dust) caused the ice age cycles.

I leave you with this gem from the celebrated poet, Henry Longfellow:
"Dust thou art, to dust returnest, was not spoken of the soul."

--Prasad

If I'm not mistaking, C is about volcanic dust and not cosmic dust, thus not really having anything to do with our question.
D, on the other hand supports the conclusion...
Although cosmic dust enters the atmosphere sometimes, it doesn't create an ice-age. This supports that the clouds need to be dense and just them being there isn't enough...
What am I missing?

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Re: Climatologists believe they know why Earth has undergone a [#permalink]

15 Sep 2014, 14:31

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prasi55 wrote:

To support the climatologists' hypothesis, you need to connect the Earth's passage through dust to the lowering of temperatures that characterises the ice age(s). C says that large amounts of dust (from wherever) have in the past caused drops in the Earth's average temperature. So there's reason to believe that this pattern might be evidenced with cosmic dust as well.

D, on the other hand, provides no such correlation. D doesn't suggest that sometimes those large rocks create dense enough clouds to cause an ice age and that sometimes they do not. At the same time, D doesn't suggest that the periodic appearance of cosmic dust DOES NOT cause corresponding drops in temperature (characteristic of the ice ages) either. D basically provides no link between the clouds or their density and the ice ages.

To your statement about the cloud density:
If non-dense clouds do not cause an ice age, it doesn't mean that dense clouds will cause one.

--Prasad

Still not getting it.
As I see it, C says that during a volcanic eruption, there is dust in the air (obviously not cosmic dust, as it's a result of the volcano) that make the temperature drop.
So we can say and speculate (just like in your explanation) that there is the option that there was an all around big volcanic eruption in the whole world that caused the ice-age, and not cosmic dust....
Right?
What am I missing?

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Re: Climatologists believe they know why Earth has undergone a [#permalink]

10 Oct 2014, 05:47

(D) Large bits of cosmic rock periodically enter
Earth’s atmosphere, raising large amounts of
dust from Earth’s surface.

raising the dust from earth- does not strengthen the topic at hand.

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Climatologists believe they know why Earth has undergone a [#permalink]

17 May 2015, 07:43

vjsharma25 wrote:

Climatologists believe they know why Earth has undergone a regular sequence of ice ages beginning around 800,000 years ago. Calculations show that Earth’s orbit around the Sun has fluctuations that coincide with the ice-age cycles. The climatologists hypothesize that when the fluctuations occur, Earth passes through clouds of cosmic dust that enters the atmosphere; the cosmic dust thereby dims the Sun, resulting in an ice age. They concede, however, that though cosmic dust clouds are common, the clouds would have to be particularly dense in order to have this effect.

Each of the following, if true, would lend support to the climatologists’ hypothesis EXCEPT:

(A) Earth did not pass through clouds of cosmic dust earlier than 800,000 years ago.
(B) Two large asteroids collided 800,000 years ago, producing a tremendous amount of dense cosmic dust that continues to orbit the Sun.
(C) Earth’s average temperature drops slightly shortly after volcanic eruptions spew large amounts of dust into Earth’s atmosphere.
(D) Large bits of cosmic rock periodically enter Earth’s atmosphere, raising large amounts of dust from Earth’s surface.
(E) Rare trace elements known to be prevalent in cosmic debris have been discovered in layers of sediment whose ages correspond very closely to the occurrence of ice ages.

Source : LSAT PrepTest 44, Q17

D. Large bits of cosmic rock periodically enter Earth’s atmosphere, raising large amounts of dust from Earth’s surface.
Therefore,earth does not enter dust zone.

G

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Re: Climatologists believe they know why Earth has undergone a [#permalink]

17 May 2015, 23:51

Conclusion:
"Dust thereby dims the Sun resulting in an ice age"

If so, the answer becomes clear

Only D gives dust without linking dimmed sun, ice age and time

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Re: Climatologists believe they know why Earth has undergone a [#permalink]

21 Feb 2016, 08:38

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Zatarra wrote:

D is the option that does not strengthen the argument
D )Large bits of cosmic rock periodically enter
Earth’s atmosphere, raising large amounts of
dust from Earth’s surface.
Nothing has been mentioned abt the rise of dust from the earths surface and how it affects temperature on Earth.

The main point in here is that D is referring to dust from the earth's surface but in the stimulus is saying clearly that is cosmic dust.
Hope this helps.

P

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Re: Climatologists believe they know why Earth has undergone a [#permalink]

21 Apr 2017, 06:57

I narrowed down between C and D but how can we completely eliminate C?

C states that volcanic eruptions spew large amounts of dust into Earth’s atmosphere while argument talks about cosmic dust

L

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Climatologists believe they know why Earth has undergone a [#permalink]

21 Apr 2017, 07:28

vjsharma25 wrote:

Climatologists believe they know why Earth has undergone a regular sequence of ice ages beginning around 800,000 years ago. Calculations show that Earth’s orbit around the Sun has fluctuations that coincide with the ice-age cycles. The climatologists hypothesize that when the fluctuations occur, Earth passes through clouds of cosmic dust that enters the atmosphere; the cosmic dust thereby dims the Sun, resulting in an ice age. They concede, however, that though cosmic dust clouds are common, the clouds would have to be particularly dense in order to have this effect.

Each of the following, if true, would lend support to the climatologists’ hypothesis EXCEPT:

(A) Earth did not pass through clouds of cosmic dust earlier than 800,000 years ago.
(B) Two large asteroids collided 800,000 years ago, producing a tremendous amount of dense cosmic dust that continues to orbit the Sun.
(C) Earth’s average temperature drops slightly shortly after volcanic eruptions spew large amounts of dust into Earth’s atmosphere.
(D) Large bits of cosmic rock periodically enter Earth’s atmosphere, raising large amounts of dust from Earth’s surface.
(E) Rare trace elements known to be prevalent in cosmic debris have been discovered in layers of sediment whose ages correspond very closely to the occurrence of ice ages.

Source : LSAT PrepTest 44, Q17

Strengthen the Argument (All EXCEPT)

A choice that fails to strengthen an argument either contradicts it or is irrelevant to it.

Four of the choices support the idea that extremely dense cosmic dust periodically blocking the sun has been the cause of each of the ice ages that Earth has suffered beginning 800,000 years ago. We need to go into the choices confident that (1) there’s a 4:1 chance—that is, a strong likelihood—that each of these choices does support the cosmic dust idea, and (2) one and only one of them either contradicts that hypothesis or falls outside its scope. Be bold as you consider each:

(A) Suppose the first cosmic dust clouds appeared 800,000 years ago. That would be a “co-incidence” in the most formal meaning of the term: two things happening together. As we know, correlation doesn’t prove causation, but a strengthener doesn’t have to prove the point; it just has to bolster it. (A) does so by connecting the first appearance of a phenomenon to the hypothesized cause of the phenomenon. Eliminate.

(B) The appearance, 800,000 years ago, of a huge (and thereafter constant) cosmic dust cloud certainly supports the hypothesis, as surely as the absence of any cosmic dust around that time would weaken it. Eliminate.

(C) draws a palpable connection between cold temperatures and atmospheric dust. Sure, it’s only a “slight” temperature drop, but maybe that’s enough to cause an ice age. Eliminate.

(D) asserts that Earth suffers cosmic dust clouds. Well, we already knew that; “cosmic dust clouds are common,” say the climatologists. (D) does NOTHING to relate those clouds to any of the factors allegedly contributing to the periodic ice ages, so (D) is the “odd man out” we seek.

We can be quite confident that (E) is another strengthener, and so it is, connecting cosmic debris—the result of cosmic dust—to the periodic nature of ice ages.

Quote:

The conclusion of this argument is that the cause of ice ages is the earth passing through cosmic dust clouds, which in turn is caused by fluctuations in the Earth's orbit around the sun. (I always thought that!). The climatologists base their argument on the fact that the occurrences of ice ages, starting 800,000 years ago has coincided with fluctuations in the Earth's orbit around the sun. The climatologists note that the clouds would have to be quite dense for this all to be true.

We're looking for an answer that does NOT strengthen the argument. (D) introduces the fact that cosmic rock periodically enters the earth's atmosphere and kicks up dust. This WEAKENS the argument in that it raises the possibility that there's another reason for the dust that causes the ice ages: it's the cosmic rock dust, NOT the fluctuations! However, there are problems with this answer as a weakener in that we'd need to do a lot of "work" to make (D) weaken: periodically would have to coincide with the ice-age cycles, the dust that is kicked up would have to be dense, and would have to reach the atmosphere - though, as one poster below suggests, perhaps we should consider anything above the earth's surface to be atmosphere! But, let's not lose sight of what we're looking for - something that does not strengthen, and regardless of whether (D) weakens or is neutral, it DOESN'T strengthen the argument.

(A) supports the connection between the clouds and the ice ages: of course there were no ice ages before then, we didn't float through any dust clouds!
(B) establishes that there is indeed a dense cloud around the sun, something the climatologists conceded needed to be true -- and answers the nagging question of why the ice ages only began in the year 800,000 b.c.e.
(C) supports the idea that dust causes a lower temperature, strengthening the argument.
(E) provides more evidence that Earth passed through a cosmic cloud around the time of the ice age.

gmatclubot

Climatologists believe they know why Earth has undergone a [#permalink]

21 Apr 2017, 07:28

GMAT Critical Reasoning (CR) Questions

Climatologists believe they know why Earth has undergone a