LSAT 80, Logical Reasoning I, Q25, LSATHacks

LR Question 25 Explanation, by LSATHacks

QUESTION TEXT: Oceanographer: To substantially reduce the amount of…

QUESTION TYPE: Necessary Assumption

CONCLUSION: We can greatly reduce the amount of carbon dioxide in the atmosphere by pumping the CO2 into the deep oceans.

REASONING: The water in the deep oceans is cool, and takes centuries to mix with the warmer water near the surface.

ANALYSIS: You should always look for concept switches. The conclusion mentions getting rid of carbon dioxide, but the evidence is about the odds of water mixing. The author is assuming that the dissolved CO2 won't travel upwards faster than the cool water does.

___________

1. The water temperature wasn't the point. The reason we're putting the CO2 in the depths is because it is far from the atmosphere.
2. This doesn't matter. Lots of things in the natural cycle trap and release CO2. So if warm water naturally releases some CO2, that's fine. The argument's point is that we're putting the CO2 into deep water, so it should take centuries for it to rise to the warm water where it may be released.
3. CORRECT. If this isn't true, then the fact about cold water's speed is irrelevant. Carbon dioxide travels upwards on its own, faster than the water.
   Negation: Carbon dioxide will escape back into the atmosphere quite quickly, much faster than the cool deep water mixes with warm water.
4. We don't care how carbon dioxide is trapped. We only care that it is trapped.
5. The argument is stronger if this isn't true! This answer says “We should pump CO2 into the ocean only for the exact reason the author says”.
   That's terrible: it eliminates the possibility of other reasons. An argument is always stronger with additional reasons. The negation opens up the possibility of other reasons, strengthening the argument.

Recap: The question begins with “Oceanographer: To substantially reduce the amount of”. It is a Necessary Assumption question. To practice more Necessary Assumption questions, have a look at the LSAT Questions by Type page.

Hi, I'm Graeme Blake

Founder of LSAThacks; I scored a 177 on the LSAT.

I created the LSAT Mastery Seminars, which are part of the Ultimate LSAT Prep Bundle

If you like the explanations you're reading I'm 100% confident you'll enjoy the courses. Satisfaction guaranteed.

---------
Updates:

For updates, sign up for my email list. I update whenever I have new posts.