Question #1064

The difference between proportions and amounts

Started by Brett-Lindsay · started 2020-07-21 06:44 · last activity 2024-05-07 01:19 · 7 replies

Hi everybody, I've noticed that a lot of people are confused by the wording in answer B. Many are reading it as meaning that the amount of Oxygen 18 is increasing. It is not saying that at all. Let's look at the wording very carefully. It states, "The CONCENTRATION of oxygen 18 in seawater is increased." While they're not 100% the same, the following words are all expressing relative amounts, so we can think of them as being similar: concentration = proportion = percentage What's happening in the ocean is that more O16 than O18 is leaving. Normally, the rain brings it all back, so the ratio stays the same. In the ice age, though, the water is not returned to the ocean - it is added to ice caps. That means that the total amount of water that is left in the ocean is decreasing. As more O16 is leaving, we could say that proportionally, more O18 is being left behind, thus skewing the original ratio by increasing the amount of O18 relative to the amount of O16. An example from real life might make it a little easier to understand. Let's say that I had 200 pens in a drawer, 100 red and 100 blue. If I took out 2 blue and 1 red at the beginning of the day, there would be one more red than blue pens in the drawer. At the end of the day, though, if I put them all back, the original ratio would be maintained. What would happen if I didn't replace the pens? There would be more red pens than blue pens, and the more days that passed, the greater the difference in number of red pens to blue pens. Note that the actual number of red pens isn't "increasing," though. The proportion of red pens to blue pens is increasing. Sorry for writing such a long post, but the concept of proportions can be hard to grasp.

Replies

  1. lexiw · 2020-09-10 02:51

    THANK YOU SO MUCH!!!

  2. allisonfarley · 2020-10-16 22:08

    Never apologize for helping ! The longer the better :D These minute details are killer !

  3. mmanetti · 2021-03-26 16:50

    Thank you! So helpful.

  4. Karen-Norris · 2021-06-11 19:37

    Well I'm slightly irked at this question. After reading the explanation I realized that the stimulus is using the word ocean and sea somewhat interchangeably and oceans and seas are not the same thing. It would have made more sense to me if the stimulus addressed ocean vapor and ocean water, not ocean vapor and sea water.

  5. Karen-Norris · 2021-06-12 00:47

    I erroneously picked C, because I made an assumption that the composition of sea vapor corresponded to the composition of Sea Water. So I thought Ocean vapor would have more Oxygen 16 and less Oxygen 18, than Sea Vapor which would have Less Oxygen 16 than Ocean Vapor and More Oxygen 18 than Ocean Vapor. I assumed (rather cloddishly) that in a normal year Sea Vapor Clouds (sea's are typically landlocked or border land as opposed to oceans) would wander over the ocean and rain down generous portions of Oxygen 18 into the ocean. But, during a glacial period, the Sea Vapor Clouds would not rain into the ocean, but would become locked into ice, thereby causing the relative proportion of Oxygen 18 in the oceans to be less.

  6. Karen-Norris · 2021-06-12 01:13

    Okay, I feel better now. Thanks for listening ;-)

  7. NULL · 2024-05-07 01:19

    Thank you! :) I too mistook concentration for amount.

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