#17 - Climatologists believe they know why Earth has

[amna.ali467]

Yes thanks so much! Couldn't see that connection by myself.

[Franny_i]

Hello friends,

I choose 'C' for this problem. I'm having trouble understanding how it supports the climatologists' hypothesis since it mentions volcanic dust as opposed to cosmic dust. 'D' I had a little trouble eliminating but I felt 'C' was the superior choice.

[Robert Carroll]

Franny,

Answer choice (C) shows a situation where a different phenomenon cools the Earth via a similar mechanism. This shows that a causal connection between "large amounts of dust in the atmosphere" and "cooler temperatures" has some independent basis. This lends some support to the idea that large amounts of cosmic dust would have a similar effect. Remember, the stimulus isn't saying that only cosmic dust will have this effect, but that cosmic dust entered the atmosphere and dimmed the Sun. If cosmic dust could have that effect, you would expect any source of dust to do it, which answer choice (C) supports.

Robert Carroll

[queenbee]

Hi
I struggled with this one because:

B says that the cosmic dust is still around today - I took that to mean that if the cosmic dust is still around today, then we should be in an ice age, which we are not. So I selected B.

But I didnt select D because I thought the fact that cosmic dust was causing dust from the earth's surface to raise, the additional dust from the earth's surface would add to the density.

Any chance you can help clarify the flaw in my logic?
Thank you!

[Adam Tyson]

The cosmic dust in answer B is still orbiting the sun, but that doesn't mean that the Earth is currently passing through it and filling the atmosphere with dust. Maybe it's just a matter of time before we pass through it again, and then a new ice age will begin. Maybe the orbits of the cosmic dust cloud and the Earth are such that they will never again intersect, and that won't cause another ice age. The cloud is still out there somewhere, but that's not what causes the ice age. It's only when the Earth passes through it that we get that effect.

B helps because it ties the start of the regular cycle of ice ages to the creation of the dust cloud. In other words, the cause and the effect happened around the same time as each other. The timing looks right, which helps, and that makes B a wrong answer.

D puts dust in the air, but does nothing to connect that dust to ice ages or lower temperatures. That's why it doesn't support the hypothesis, and is therefore the correct answer. To help, it would have to also say something about the temperature dropping when this happens, like answer C does.

[ashutosh_73]

The cosmic dust in answer B is still orbiting the sun, but that doesn't mean that the Earth is currently passing through it and filling the atmosphere with dust. Maybe it's just a matter of time before we pass through it again, and then a new ice age will begin. Maybe the orbits of the cosmic dust cloud and the Earth are such that they will never again intersect, and that won't cause another ice age. The cloud is still out there somewhere, but that's not what causes the ice age. It's only when the Earth passes through it that we get that effect.

B helps because it ties the start of the regular cycle of ice ages to the creation of the dust cloud. In other words, the cause and the effect happened around the same time as each other. The timing looks right, which helps, and that makes B a wrong answer.

Hi Adam, During timed condition, i was down to (B) and (D). I had two concerns, which made be choose (B) over (D):

1. (B) says ''continues to orbit the Sun'', hence we should have multiple ice-age cycles.

But you explained above that ''may be earth has not crossed the dust cloud's path yet'' OR ''maybe earth has a different''. So it answers my first concern.

2. Stimulus says ''when the fluctuations occur, Earth passes through clouds of cosmic dust''
While evaluating (B) i thought:
So, its not the fluctuations which caused the cosmic dust, rather it was the asteroids. Therefore (B) gives us a alternate cause.

In the hindsight, i now see that option never says, ''Fluctuation caused the cosmic dust''.
Rather (B) presents a mere correlation. So, its possible that both fluctuations and cosmic dust were caused by ''Asteroids''

Asteroids impact --> Fluctuations + Cosmic dust ---> Ice ages.

Hence, it strengthen the argument. Is my understanding correct OR i am being delusional?

[Dana D]

Hey Ashutosh,

The thing to key in here is that climatologists are citing dust in the atmosphere as the reason for the Ice Ages, because it is the significant atmospheric dust which dims the Sun and causes an Ice Age. Therefore answer choice (B) supports the hypothesis because it is also pointing to evidence of dense atmospheric dust. The cause of the Ice Age cycles isn't cosmic dust itself or fluctuations or anything else - the cause is the dimming of the Sun. Cosmic dust is just one way the Sun could be dimmed and a subsequent Ice Age triggered.

Answer (D), in contrast, is talking about dust on the Earth's surface - but it doesn't matter how dusty things get down here, unless that dust is getting into the atmosphere and is going to dim the Sun's warmth, it doesn't strengthen the argument about the cause of Ice Ages.

[jhobgood16]

This is helpful. I get why D is incorrect, but I was reading C as an alternate cause for the ice age. I thought that a few degrees drop from the volcano would be another cause for the ice age, instead of the cosmic dust entering the Earth's atmosphere. Because the stimulus didn't specify how many degrees of a drop is needed for an ice age, I thought a few degrees would be enough for the volcano option. But the stimulus would have mentioned that since it's not common knowledge, right?

[Dana D]

Hey Jhobgood,

The right answer here would be one that weakens the climatologists' argument that the cosmic dust dimming the Sun results in an ice age. You are correct in thinking that if we introduced an alternative cause, that would weaken this argument, but answer choice (C) fails to do that. Notice answer choice (C) says that temperature drops slightly but does not specify what 'slightly' means - we're talking about inducing an ice age here, so a 1 degree drop in temperature could be a 'slight drop' in temp but would not correlate to ice age levels of cold. Furthermore, this slight temperature drop is a precursor to the volcano spewing large amounts of dust into the atmosphere, which likely dims the Sun and results in the ice age, so answer choice (C) does not weaken the argument.

Hope that helps!