LSAT Explanation PT 43, S3, Q13: Up until about 2 billion years
LSAT Question Stem
Which one of the following, if true, most helps to resolve the apparent discrepancy described above?
Logical Reasoning Question Type
This is a Paradox question.
Correct Answer
The correct answer to this question is A.
LSAT Question Complete Explanation
To better understand this LSAT problem, let's break down the information in the passage and simplify the concepts. The passage tells us that 2 billion years ago, the sun was 30% dimmer than it is now. If the sun were that dim today, our oceans would be completely frozen. However, fossil evidence shows that life and liquid water existed as early as 3.8 billion years ago. This creates an apparent discrepancy: if the sun was dimmer, how could liquid water exist?
Think of it like this: imagine you have a room with a heater (the sun) and a blanket (the atmosphere). If the heater is not strong enough, the room would be too cold for people to live comfortably. However, if the blanket is thicker and retains more heat, people could still live comfortably despite the weaker heater. This is the kind of explanation we're looking for in the answer choices.
Now, let's analyze the answer choices based on the question type, which is a Paradox question. The question asks us to resolve the apparent discrepancy described in the passage.
Answer choice (A): This answer choice is correct. It explains that our atmosphere currently holds in significantly less heat than it did 3.8 billion years ago. This means that even though the sun was dimmer back then, the atmosphere was able to retain more heat, allowing liquid water to exist. This is like our room example, where the thicker blanket compensates for the weaker heater.
Answer choice (B): This answer choice suggests that the liquid water present 3.8 billion years ago later froze and then melted again about 2 billion years ago. While this may be true, it doesn't explain how liquid water could exist when the sun was dimmer. It merely reaffirms that there was liquid water at some point in the ancient era but doesn't resolve the discrepancy.
Answer choice (C): This answer choice talks about a significant source of heat other than the sun contributing to the melting of ice sheets approximately 2 billion years ago. While it may seem promising, it only addresses one time period and doesn't explain how liquid water could have existed during the ancient era (3.8 billion years ago) when the sun was dimmer.
Answer choice (D): This answer choice suggests that certain regions of the ocean remained frozen until much more recently than 2 billion years ago. However, it doesn't explain how liquid water could have been present at all 3.8 billion years ago when the sun was at least 30% dimmer than it is now.
Answer choice (E): This answer choice, if true, would actually worsen the discrepancy. If a larger portion of the globe is ice-covered, more of the sun's heat is reflected and not absorbed by the earth. This would make it even more challenging to explain the presence of liquid water 3.8 billion years ago under conditions that would not allow for liquid water today.
In conclusion, the correct answer choice is (A), as it provides a clear explanation for the apparent discrepancy by stating that the atmosphere held in more heat 3.8 billion years ago, compensating for the dimmer sun and allowing liquid water to exist.