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# PT1.S3.Q11 - Water vapor evaporated from the ocean..

Monthly Member
edited March 20 17 karma

Admin Note: Edited title. Please use the format: "PT#.S#.Q# - brief description of the question."

• Monthly Member
210 karma
1. So basically the first premise is saying when water evaporates there's more Oxygen-16 in proportion to Oxygen-18 (since its heavier), but it doesn't really effect anything because after it evaporates it just comes back down as rain.

2. Then we get a 'however', telling us that during the ice age a large amount of rain fell on the ice, and became trapped (or locked in place).

So Imagine a pool that filled with 500 beach balls (Oxygen-16) and 500 heavy medicine balls (Oxygen-18).

One day you take a big scoop from the top of pool taking out 100 balls. What would you expect the scoop to be comprised of?

There would probably be a lot of beach balls and not a whole lot of the heavy medicine balls, since they would sink to the bottom. Lets say it would probably be like 98-99 beach balls (Oxygen-16) and 1-2 medicine balls (Oxygen-18).

Okay, but now it "rains" so you put back all 100 of the the balls you took out back into the pool.

The next day you take another scoop of 100 balls, what would happen? You would get almost exactly the same proportion and original composition starting composition of the pool (500 light balls, 500 heavy balls), with each scoop being roughly 98-99 beach balls (Oxygen-16) and 1-2 medicine balls (Oxygen-18). If you put all the balls back in after each scoop and repeat the proportions of the scoops would never change and the composition of the pool would stay exactly the same ("this is the no effect on the overall composition of the ocean").

Now for the "Ice Age". Imagine instead of putting all the balls back into the pool ("it raining") you kept 80 of them to keep locked in your room and threw 20 of them back into the pool ("large amount of precipitation falls on the ice caps trapping them as ice").

So lets say you repeated this this for a period of 5 days. What would happen? Since you are taking way more of the light beach ball out on each scoop. After each scoop the proportion of heavy medicine balls remaining in the pool would increase relative to the starting 50/50 ratio. By the end of day 5 you would have an overwhelming amount/proportion of medicine balls (Oxygen-18) compared to the whole.