Inset without labels (IMAGE) Stanford University Caption Showers of high energy particles originating from the sun and our galaxy collide with nitrogen and oxygen in the upper atmosphere. At ground level, the shower is dominated by magnetically polarized muons. At the protobiological site, nucleic acids assumed either a right-handed or left-handed helical conformation. The magnetically polarized radiation preferentially ionized one type of 'handedness' leading to a slightly different mutation rate between the two mirror proto-lifeforms. Over time, right-handed molecules out-evolved their left-handed counterparts. Credit Simons Foundation Usage Restrictions Image may only be used with appropriate caption or credit 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.