Hall's Cave (IMAGE) University of Houston Caption Researchers relied upon isotope analysis of sediments collected from Hall's Cave, located in the Texas Hill Country, to determine a new explanation for a dramatic period of global cooling about 13,000 years ago. Credit Nan Sun, University of Houston 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.