Oxygen Isotopic Fractions (image) DOE/Lawrence Berkeley National Laboratory Caption A three-isotope plot of oxygen begins with the Earth-standard mean ocean water ratio (SMOW). Departures from SMOW in the fractions of oxygen-17 (vertical axis) and oxygen-18 (horizontal axis) fall along a slope of about one-half, a sign of processes solely dependent on the differing isotope masses. In meteorites and other interplanetary sources, differing oxygen ratios fall on a different slope, signaling chemical processes as well as physical ones. Credit University of California at San Diego, Lawrence Berkeley National Laboratory Usage Restrictions None 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.