June 1991 LSAT Section 3 Question 11

Water vapor evaporated from the ocean contains a greater proportion of oxygen–16 and a smaller proportion of the heav...

ankita96 on August 11, 2020

Ans Choice B

Hi, The stimulus says that the ocean contains a more proportion of O-16 to O18 than sea water. Now if the rain get caught in ice, how does only 0-16 decrease. the whole proportion should be getting caught right?

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shunhe on August 11, 2020

Hi @ankita96,

Thanks for the question! So to be specific, it’s the water vapor that evaporates from the ocean that has a higher proportion of O16 to O18 than seawater. So let’s say that this is 75% 25% O16 to O18. And then this gets caught in ice. So both decrease. O16 and O18 will both decrease; as you’ve pointed out, it’s not the case that just O16 decreases. So that whole proportion does get caught. But that means water that’s 75% O16 and 25% O18 gets caught. So proportionally, more O16 is getting caught. And that’s O16 that isn’t getting returned to the ocean. So O18’s concentration in seawater will increase, since O16 is getting trapped more than O18.

Hope this helps! Feel free to ask any other questions that you might have.