Mean Ocean Water and Troilite (image) DOE/Lawrence Berkeley National Laboratory Share Print E-Mail Caption The "natural" fractionation of oxygen's three stable isotopes, based on the average in ocean water, is 99.762 percent oxygen-16, 0.038 oxygen-17, and 0.2 percent oxygen-18. The standard ratio of the four stable isotopes of sulfur is 95.02 percent sulfur-32, 0.75 percent sulfur-33, 4.21 percent sulfur-34, and 0.02 percent sulfur-36. The standard comes from a form of pure iron sulfide called troilite (inset) found in Diablo Canyon iron meteorites whose parent, a fragment of which is shown at upper left foreground, created Meteor Crater in Arizona. Credit Lawrence Berkeley National Laboratory, Wikimedia Commons, KD Meteorites Usage Restrictions With credit as given Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.