LSAT 131 – Section 2 – Question 25

LSAT 131 - Section 2 - Question 25

December 2009

You need a full course to see this video. Enroll now and get started in less than a minute.

Request new explanation

Target time: 1:37

This is question data from the 7Sage LSAT Scorer. You can score your LSATs, track your results, and analyze your performance with pretty charts and vital statistics - all with a Free Account ← sign up in less than 10 seconds

Question
QuickView		 Type Tags Answer
Choices		 Curve Question
Difficulty		 Psg/Game/S
Difficulty		 Explanation
PT131 S2 Q25
+LR
Weaken +Weak
Causal Reasoning +CausR
A
11%
162
B
54%
167
C
11%
160
D
9%
159
E
15%
162
155
164
173
 +Hardest 147.936 +SubsectionMedium

J.Y.’s explanation

You need a full course to see this video. Enroll now and get started in less than a minute.

About 3 billion years ago, the Sun was only 80 percent as luminous as it is currently. Such conditions today would result in the freezing of Earth’s oceans, but geological evidence shows that water rather than ice filled the oceans at that time. Heat is trapped within Earth’s atmosphere through the presence of carbon dioxide, which, like methane, is a “greenhouse gas.” Only if the level of greenhouse gases were higher 3 billion years ago than it is today would Earth have retained enough heat to keep the oceans from freezing. It is likely, therefore, that the level of carbon dioxide in the atmosphere was significantly higher then than it is today.

Summarize Argument
The author concludes that the level of carbon dioxide in the atmosphere was much higher 3 billion years ago than it is today. This is because we know that the ocean was liquid 3 billion years ago, and that required the level of greenhouses to be higher 3 billion years ago than it is today.

Notable Assumptions
The author assumes that if greenhouse gases were higher 3 billion years ago, carbon dioxide levels must have been higher 3 billion years ago. This overlooks the possibility that there were other greenhouse gases that were higher back then, while carbon dioxide levels stayed the same or were even lower.

A
Sufficient heat to keep the oceans liquid 3 billion years ago could not have been generated through geological processes such as volcanic activity.
We already know that greenhouse gases were higher 3 billion years ago, which is what helped keep the Earth warmer. The original source of the heat doesn’t change the fact that we know greenhouse gases were higher.
B
Geological studies indicate that there is much less methane in Earth’s atmosphere today than there was 3 billion years ago.
This raises the possibility that the greater levels of greenhouse gases 3 billion years ago were due to higher levels of methane. Carbon dioxide could have been equal or lower than it is today, because methane was higher.
C
Geological evidence indicates that the oceans contained greater amounts of dissolved minerals 3 billion years ago, but not enough to alter their freezing points significantly.
We already know that the ocean was liquid and that this proves greenhouse gases were higher 3 billion years ago. The freezing point of water doesn’t change how we interpret these facts.
D
The increase in the Sun’s luminosity over the past 3 billion years roughly coincided with an increasing complexity of life forms on Earth.
How the sun’s brightness correlates with the complexity of life is irrelevant. The argument concerns levels of greenhouse gases and whether higher levels of greenhouse gases imply higher levels of carbon dioxide.
E
Because the distance from Earth to the Sun has not changed significantly over the last 3 billion years, the increase in the Sun’s luminosity has resulted in more radiation reaching Earth.
We already know the Earth was liquid and that this proves greenhouse gases were higher 3 billion years ago. Levels of radiation don’t change these facts or how we interpret them. The argument concerns whether higher levels of greenhouse gases imply higher carbon dioxide levels.

Take PrepTest

Review Results

LSAT PrepTest 131 Explanations

Section 1 - Logical Reasoning

Section 2 - Logical Reasoning

Section 3 - Logical Reasoning

Section 4 - Reading Comprehension

Get full LSAT course

Leave a Reply