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Climatologists believe they know why Earth has undergone a

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Climatologists believe they know why Earth has undergone a [#permalink] New post 12 Mar 2011, 20:31
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40% (02:55) correct 60% (01:52) wrong based on 156 sessions
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.
[Reveal] Spoiler: OA

Last edited by vjsharma25 on 12 Mar 2011, 23:19, edited 1 time in total.
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Re: Climatologists belief [#permalink] New post 12 Mar 2011, 22:15
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 belief [#permalink] New post 12 Mar 2011, 22:33
Hmmm.....not every CR is that easy :-)
Think again!!
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Re: Climatologists belief [#permalink] New post 12 Mar 2011, 22:38
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 belief [#permalink] New post 12 Mar 2011, 22:43
+1 kudos for the question
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Re: Climatologists belief [#permalink] New post 12 Mar 2011, 22:47
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 belief [#permalink] New post 12 Mar 2011, 22:58
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 belief [#permalink] New post 12 Mar 2011, 23:15
E uses "rare" trace. Its the prima evidence.

It has to be D.
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Re: Climatologists belief [#permalink] New post 14 Mar 2011, 00:32
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 belief [#permalink] New post 24 Apr 2014, 08:39
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
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Re: Climatologists believe they know why Earth has undergone a [#permalink] New post 30 May 2014, 14:01
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?

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J
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Climatologists believe they know why Earth has undergone a [#permalink] New post 30 May 2014, 20:42
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
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Re: Climatologists believe they know why Earth has undergone a [#permalink] New post 10 Jun 2014, 10:05
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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Climatologists believe they know why Earth has undergone a [#permalink] New post 10 Jun 2014, 10:44
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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
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Climatologists believe they know why Earth has undergone a   [#permalink] 10 Jun 2014, 10:44
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