#11 - Water vapor evaporated from the ocean contains a

[Sherry001]

Hello ;
I would appreciate your help with this ugly question. It makes sick .

1- water vapor evaporated from the ocean contains a greater percentage of oxygen 16 and a smaller percentage of oxygen 18.

2- normally this phenomenon has no effect on the overall composition of the ocean because the evaporated water returns back through participation.

3- during an ice age however a large amount of precipitation falls on ice caps, where it is trapped as ice.

So we're asked what could we infer from a typical ice age: my pre phrase was something like " so during an ice age this phenomenon affects the overall composition of the lake .. Maybe it doesn't return back into the ocean . That's why D was attractive to me.

A)were only given info about the oxygen percentages of vapor.
B) how can this be ? Can it not be that oxygen 16 was reduced and maybe that's why the composition changed?
C)interglacial period is not supported in the stimulus,
D)seemed attractive because of my prephrase. And I still can't get rid of this .
E)completely irrelevant.


Thanks so much
Sherry

[Lucas Moreau]

Hello, Sherry,

I can see how you would get to answer choice D, I really can.

The problem with D is that it sounds reasonable but it goes too far. The stimulus merely says that "a large amount of precipitation" falls on ice caps, it doesn't say anything about what percentage of precipitation falls on ice caps. D states that more precipitation falls on ice caps or other kinds of land than on water during ice ages, which isn't supported by the question. "A large amount" could still be a tiny percentage compared to the total precipitation in the world.

With answer choice B, we have to think about the evaporation process. If, as the stimulus states, evaporated seawater contains more oxygen-16 and less oxygen-18 than seawater, then the inverse of this is also true: seawater contains more oxygen-18 and less oxygen-16 than evaporated seawater. It's almost like a contrapositive.

Since more of this oxygen-16-rich and oxygen-18-poor evaporated seawater fails to return to the ocean, instead hardening into ice caps, it therefore follows that the ocean's total oxygen-18 concentration would increase as the ice age continues, thus proving answer choice B to be correct.

Hope that helps,
Lucas Moreau

[Sherry001]

Aha !!! You made it click for me !
Thank you so much !

[akanshalsat]

Hello I don't understand this question at all. You all explained it by saying "evaporated SEA WATER compared to seawater" but it says evaporated OCEAN WATER compared to sea water. I'm also just very confused in general how to get the correct answer

[Adam Tyson]

I get your confusion there, akanshalsat. In common usage, "seawater" IS "ocean water". We often use those words interchangeably, like referring to the "seafloor" and calling the beings that live in the ocean "sea creatures". Oceangoing vessels can be referred to as seaships, and we visit the seashore when we go to the beach at the Outer Banks or the Jersey Shore or Malibu. My son is in the Navy, and they call him a Seaman, even though he will most likely be traveling across oceans. So, treat those terms as being the same thing, and this should get much easier for you!

The thing to pay attention to here is the numbers issue, about proportions. The evaporated water has a different proportion of stuff than the water itself does, so as it evaporates it changes the concentration of the water by taking relatively more of one thing than another. If that stuff in the water vapor doesn't end up back where it started, the overall mixture in the ocean changes.

I hope you can sea that now!

[harvoolio]

Adam,

Ugh. I did the same thing that the other poster did in that I read that we are are only told about vapor escaping from the ocean so we can only conclude that during an ice age the concentration of oxygen-18 in the ocean is increased but do not know about seawater. I was able to knock out C, D and E but uncertain about A so I selected it given I thought B was wrong.

What is worse is that I was born and raised in the Jersey Shore.

I am a little concerned because I just listened to the presentation on what to expect for the June 2018 LSAT and apparently word ambiguity has increased recently so my problems with these types of questions might increase too. My issues are usually with science questions and not having basic knowledge — I just recently discovered that bird migration ranges refers to the respective ranges in breeding and wintering seasons and not the range (distance) between those places.

Any advice? My guess is word rigidity (for lack of a better phrase) depends upon the respective strength in other answers.

Thanks.

[Adam Tyson]

I'm a bit late for you here, harvoolio - sorry about that! My advice would have been - and still is - to be flexible, use context, and always consider the less commonly used definition of a word.

I hope this didn't prove to be a problem back in June! Let us know?

[dbrowning]

Contrary to what normally happens on science-related stimuli, I missed this question only because I knew that there is a difference between an ocean and a sea, namely "seas are smaller than oceans and are usually located where the land and ocean meet. Typically, seas are partially enclosed by land". I want to ask how I can avoid this mistake again, but it seems unreasonable for LSAC to expect us to things that are different even though people use them interchangeably incorrectly. I would have been quite upset had I lost points for this on a real LSAT.

I ended up eliminating every answer choice and chose A because I was certain all other answers were incorrect, though my intuition led me to suspect B. In the future, when I have eliminated all answers (and have come back to the question on a second pass), what is a good strategy for re-assessing a question like this?

[Adam Tyson]

When I run into that situation, dbrowning, my approach is to be "forgiving" of the answers on the second pass. First, rather than just deciding which of my "dead" answers I will resurrect ("zombie answers" in my parlance), I bring ALL of them back for a second look, and the second time I sort them into losers or contenders I am hesitant to kill an answer without having a clear reason for doing so. I KNOW that one of the answers that I previously killed is correct, so this time around I am looking for some wiggle room, some reason to keep an answer around a little while longer. That includes thinking about different interpretations of key words and phrases, numeric ideas (pay attention to "many" and "some" and "most", etc.), words indicating degree of certainty (must vs probably vs could) and facts vs opinions (must vs should).

In short, when all five answers are initially identified as losers, bring them all back as contenders rather than making an argument for bringing just one of them back. Raise the bar higher for what it takes to kill an answer. Be willing to accept bad answers if you can see the case for one being less bad than the other four.

And sometimes, we just have to guess and move on, and maybe take the L.

[relona]

I still don't really understand why B is correct. I understand the contrapositive of the oxygen-16 and oxygen-18 in seawater as opposed to evaporated seawater. I'm wondering why that would cause an increased concentration of oxygen-18 in seawater. When the evaporated seawater usually returns to the ocean, does it dilute the oxygen-18 already in the seawater?

Thanks