The relative concentrations of ¹⁸O vs ¹⁶O in shells and in ice are used as climate proxies. The main process that drives the largest of the signals in the ocean is what we call fractionation during evaporation. That the heavier H₂¹⁸O molecules have a more difficult time escaping the water surface (evaporating) than the lighter more abundant H₂¹⁶O molecules means that they get left preferentially behind in the water. This question relates to why this happens. The temperature of a liquid measures the mean kinetic energy of the molecules in that liquid. Kinetic energy E = ½ M v², where M is the mass of the object, and v its speed. If the kinetic energies of the two isotopes of water mentioned above are equal, but they have different masses, how different are their speeds? Report your answer in terms of % difference. write out the formula for each kinetic energy of each, and set them equal. You will then see that things like the ½ cancel out, and it will also become independent of the units you use for the mass (so you can just use the atomic weight of each)). You will see that the effect is subtle. It gives the light isotope just a little edge in escaping more efficiently.