Earth Collision Artist Concept (IMAGE) Southwest Research Institute Caption This artist's concept shows a giant impact similar to the one 4.5 billion years ago that scientists think created the Earth-Moon system. Southwest Research Institute scientists combined dynamical, thermal, and chemical models of the Moon's formation to explain the relative lack of volatile elements in lunar rocks, when compared to those of Earth. Credit Image Courtesy of NASA/JPL-Caltech Usage Restrictions Image Courtesy of NASA/JPL-Caltech 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.