LSAT 43, Logical Reasoning II, Q13, LSATHacks

LR Question 13 Explanation, by LSATHacks

QUESTION TEXT: Up until about 2 billion years ago, the sun was 30 percent…

QUESTION TYPE: Paradox

ANALYSIS: We know three things:

1. The sun was 30% dimmer as recently as 2 billion years ago.

   Take note that the stimulus says “up until about 2 billions years ago”, meaning that it was dim much earlier than 2 billion years ago as well.

2. If the sun were that dim today, the oceans would be frozen.
3. Yet 3.8 billion years ago, the oceans were not frozen.

Common sense is important here. The sun is not the only thing that heats the earth…otherwise we would be much colder at night. Think back to science class, and note that heat from the earth’s core and heat retained by the atmosphere are also important.

___________

1. CORRECT. This resolves the paradox. If the atmosphere held more heat 3.8 billion years ago, then less sunlight would be required to keep the oceans from freezing.
2. This is tempting, but since the stimulus says the sun was dim “up until about 2 billion years ago,” it implies it was also dim earlier than that, including 3.8 billion years ago.
3. This doesn’t explain why there was liquid 3.8 billion years ago. Also note that “contributed to” is very vague, and could be a miniscule contribution.
4. This tells us nothing. Certain regions of ocean are still frozen today, such as the Arctic. The main point is that 3.8 billion years ago there was some liquid capable of supporting life.
5. This would make the earth even colder, which doesn’t help explain why there was unfrozen liquid.

Recap: The question begins with “Up until about 2 billion years ago, the sun was 30 percent”. It is a Paradox question. Learn how to master LSAT Paradox questions on the LSAT Logical Reasoning question types page.

Hi, I'm Graeme Blake

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