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Using isotopes to answer fundamental questions:

Stable isotopes, on the other hand, do not undergo radioactive decay and they're actually much more common than radioactive isotopes but they haven't received as much attention because they don't do anything for us energy wise. Most elements are represented by at least two isotopes, sometimes more. An example is oxygen where we have the overwhelmingly abundant Oxygen-16 atom--and most of the oxygen on the planet is Oxygen-16 of course, that's what we're breathing--there is the extremely rare Oxygen-17 which we'll ignore for the rest of our talk. It's so rare that it doesn't really figure into our calculations. And then there's the somewhat more abundant, moderately abundant, Oxygen-18. And that's what we'll be relying on today.

These isotopes are essentially identical chemically. There are very, very minor differences and only the best of chemists can detect this. But physically, they can behave quite differently. And they behave differently, of course, because they have different weights and masses. I'll illustrate some of these differences to I can explain to you why this is so important to our work.

This is the oxygen isotopic cycle. It's a simplification of what's really a complex process because of weather patterns. But this is basically how it works. Within the ocean, we have a mixture of water molecules. They're water-16 molecules and water-18 molecules. Water-16 of course is much more abundant than water-18, simply because Oxygen-16 is more common than Oxygen-18. Now, during evaporation of surface waters in the ocean and sub-tropical and tropical regions, oxygen, water-16 molecules evaporate preferentially, simply because they're lighter and they require less energy for evaporation. Therefore, the clouds that form as a result of this process are said to be depleted in Oxygen-18 or enriched in Oxygen-16.


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