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Updated on: 13 Mar 2011, 00:19
Originally posted by vjsharma25 on 12 Mar 2011, 21:31.
Last edited by vjsharma25 on 13 Mar 2011, 00:19, edited 1 time in total.
Last edited by vjsharma25 on 13 Mar 2011, 00:19, edited 1 time in total.
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D
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
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44% (02:26) correct
56%
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wrong
based on 1924
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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
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
10 Jun 2014, 11:44
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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
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
30 May 2014, 21:42
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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
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
