Planet outgassing (IMAGE) University of California - Santa Cruz Caption The early atmospheres of rocky planets are thought to form mostly from gases released from the surface of the planet as a result of the intense heating during the accretion of planetary building blocks and later volcanic activity early in the planet's development. Credit Illustration by Dan Durda/Southwest Research Institute Usage Restrictions For use only with news coverage of this research 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.