Ethiopia's Chilga and Mush Valley (IMAGE) Southern Methodist University Caption Fossil leaves from prehistoric plants collected from the Ethiopian Highlands of Chilga and Mush River Valley tell scientists how much carbon dioxide was present in the atmosphere millions of years ago. (Credit SMU) Credit SMU Usage Restrictions Please credit 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.