Fossil Specimens (IMAGE) California Institute of Technology Caption The researchers analyzed the chemistry of fossils to determine the temperature during the Late Ordovician period. Shown are fossilized shells, brachiopods, trilobites, and gastropods, with a hammer for scale. Credit Woody Fischer 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.