LSAT 117 – Section 4 – Question 17

LSAT 117 - Section 4 - Question 17

October 2004

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Question QuickView	Type	Tags	Answer Choices	Curve	Question Difficulty	Psg/Game/S Difficulty	Explanation
PT117 S4 Q17	+LR	Except +Exc Strengthen +Streng Causal Reasoning +CausR	A 14% 158 B 6% 159 C 27% 161 D 48% 164 E 5% 157	150 163 176	+Hardest	147.423 +SubsectionMedium

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.

Summarize Argument: Phenomenon-Hypothesis

The author hypothesizes that the regular sequence of ice ages Earth has experienced since 800,000 years ago are caused by Earth’s passing through clouds of cosmic dust. According to this theory, the cosmic dust enters Earth’s atmosphere, which dims the sun, causing an ice age.

Notable Assumptions

The author assumes there’s no other explanation for what causes Earth’s regular sequence of ice ages. The author assumes that the occurrence of ice ages is correlated with Earth’s passage through clouds of cosmic dust.

Earth did not pass through clouds of cosmic dust earlier than 800,000 years ago.

This strengthens by defending the argument from the possibility that passage through cosmic dust occcurred before the ice ages starting to occur.

Two large asteroids collided 800,000 years ago, producing a tremendous amount of dense cosmic dust that continues to orbit the Sun.

This helps establish that the dense cosmic dust the author’s hypothesis requires actually exists and correlates with the beginning of the ice ages.

Earth’s average temperature drops slightly shortly after volcanic eruptions spew large amounts of dust into Earth’s atmosphere.

This strengthens by showing that dust in Earth’s atmosphere can reduce Earth’s average temperature. This makes the author’s theory about dust causing ice ages more plausible. Although (C) is about volcanic dust, it still shows that dust in atmosphere can cool the Earth.

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

(D) tells us that cosmic rock periodically enters the atmosphere. But does the Earth get colder after this happens? We don’t know. Do these periodic entries of cosmic rock coincide with Earth’s ice ages? We don’t know. (D) has no impact.

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.

This provides evidence of a correlation between cosmic debris and the occurrence of ice ages.

LSAT 117 – Section 4 – Question 17

LSAT 117 - Section 4 - Question 17

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LSAT PrepTest 117 Explanations

Section 1 - Reading Comprehension

Section 2 - Logical Reasoning

Section 3 - Logical Reasoning

Section 4 - Logical Reasoning

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