Thure Cerling, University of Utah (IMAGE) University of Utah Caption University of Utah geochemist Thure Cerling developed a new way to measure ancient tree cover using carbon isotopes in fossil soils. In a study in the journal Nature, he used the method to show that grassy, tree-dotted savannas prevailed at most East African sites where human ancestors and their ape relatives evolved during the last 6 million years. Credit Lee J. Siegel, University of Utah. Usage Restrictions None 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.