Antarctica Ice Core Sample (IMAGE) Rice University Caption Rice University researchers and collaborators used ice cores, like the one shown here from Antarctica, in combination with atmospheric chemistry models to establish an upper limit for the increase in ozone levels in the lower atmosphere since 1850. Credit Photo by Jeff Fitlow/Rice University Usage Restrictions Must credit: "Jeff Fitlow/Rice University" License Licensed content 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.