Critical Reasoning

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.

I believe it should be D as it clearly says that large amounts of dust is generated but if we look at E it talks about the rare trace of elements known to be prevalent in cosmic debris that has been discovered and correspond to occurence of ice ages.

I understand that A, B and C all strengthen the argument but I am confused between D and E.

Can anyone please explain this one.

Any take on this one?

Cheers!

I think it is E D actually strengthen the argument Large bits of cosmic rock periodically enter
Earth’s atmosphere, raising large amounts of dust from Earth’s surface

the clouds would have to be particularly dense in order to have this effect.

so large dense of cloud lead to iceage when earth passes through

left with E which speaks about 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.-statements above does not support why earth has undergone regular sequence of ice age

I would go with D. D states that large rock periodically enters earths atmosphere raising large amout of dust from the earth but that does not in any way suggest that this rock entering the atmosphere event coincided with previous ice ages or the amout of dust from earth was large enough to cover the sun resulting in an ice age.

IMO, E actually helps climatologists conclusion that cloud of cosmic dust might be responsible for previous ice ages on earth.

I would go with D. D states that large rock periodically enters earths atmosphere raising large amout of dust from the earth but that does not in any way suggest that this rock entering the atmosphere event coincided with previous ice ages or the amout of dust from earth was large enough to cover the sun resulting in an ice age.

IMO, E actually helps climatologists conclusion that cloud of cosmic dust might be responsible for previous ice ages on earth.

ssgmatter 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.

D is, indeed, the correct choice.

A very common argument structure that we see in CR is causation; the argument basically boils down to one thing has caused another.

In this case, the hypothesis is that passing through cosmic dust clouds caused the ice ages.

The most common weakener for causal arguments is an alternative cause: if we find another plausible explanation, we weaken the author's.

D gives us exactly that - it suggests that the cause of the ice ages isn't cosmic dust clouds, it's cosmic rocks impacting the earth and throwing up earthly dust clouds.

Since D is a weakener, it's the correct answer to a "strengthen except" question.

As an aside, the clear moral of this story is that the cosmos is out to get us!

How can C strengthen the argument ? There is no discussion about a volcanic activity in the passage. And C also gives an alternate explanation for lowering of temperature.. Can anyone please explain this ?

I am not able to digest D.
The passage says that ICE age is caused because cosmic dust dims the sun.. We want to find a choice which will not support this hypothesis..
(D) Large bits of cosmic rock periodically enter Earth's atmosphere, raising large amounts of dust from Earth's surface..
This is just supporting the argument that because of cosmic dusts (here dusts comes from earth's surface because of cosmic rocks entering atmosphere... but finally it dims the sun and causing ice age... so ultimately sun gets dim because of cosmic rocks)

(C) Earth’s average temperature drops slightly shortly after volcanic eruptions spew large amounts of dust into Earth’s atmosphere
Here, there is no mention of any cosmic effect causing dust to dim the sun. This is not supporting the argument at all.

Hence, answer should be C ?

When Stuart said D is the right answer, you mean in your opinion D is right or you know D is right ?

pops wrote:I am not able to digest D.
The passage says that ICE age is caused because cosmic dust dims the sun.. We want to find a choice which will not support this hypothesis..
(D) Large bits of cosmic rock periodically enter Earth's atmosphere, raising large amounts of dust from Earth's surface..
This is just supporting the argument that because of cosmic dusts (here dusts comes from earth's surface because of cosmic rocks entering atmosphere... but finally it dims the sun and causing ice age... so ultimately sun gets dim because of cosmic rocks)

(C) Earth’s average temperature drops slightly shortly after volcanic eruptions spew large amounts of dust into Earth’s atmosphere
Here, there is no mention of any cosmic effect causing dust to dim the sun. This is not supporting the argument at all.

Hence, answer should be C ?

Cosmic dust means cosmic dust, not earth dust. When you say "here dust comes from earth's surface", you're saying that the ice age is caused by earthly dust, not cosmic dust, thereby weakening the hypothesis. Cosmic rock does not equal cosmic dust.

The hypothesis is, in general, that dust in the atmosphere caused the ice ages. (C) supports this theory by providing general support for the whole concept of dust cooling the earth. After all, if dust in the atmosphere didn't cool the earth, then the whole hypothesis makes no sense.

So, even though (C) doesn't directly support that cosmic dust is responsible, it supports a necessary prerequisite of that theory - that dust in the atmosphere can have a cooling effect.

When Stuart said D is the right answer, you mean in your opinion D is right or you know D is right ?

I meant both!