http://en.wikipedia.org/wiki/Isotopes_of_oxygen

"The isotopic composition of oxygen atoms in the Earth's atmosphere is 99.759% 16O, 0.037% 17O and 0.204% 18O.[10] Because water molecules containing the lighter isotope are slightly more likely to evaporate and fall as precipitation[11], fresh water and polar ice on earth contains slightly less (0.1981%) of the heavy isotope 18O than air (0.204%) or seawater containing (0.1995%). This disparity allows analysis of temperature patterns via historic ice cores."

你老还是看了以后再开牙。要不然你离质疑相对论也不远了。 :)