Cosmic Impact, Dartmouth Geochemist Mukul Sharma (image) Dartmouth College Caption Using a binocular microscope, Dartmouth geochemist Mukul Sharma examines impact-derived spherules that he and his colleagues regard as evidence of a climate-altering meteor or comet impact 12,900 years ago. Credit Eli Burakian Usage Restrictions The photographer must be credited. 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.