The Bio in Bioprecipitation (IMAGE) Montana State University Caption Montana State University professor David Sands holds a petri dish with bacteria believed to play a major role in causing rain and snow. Credit MSU photo by Kelly Gorham 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.