Moon Formation Still Shot (IMAGE) Carnegie Institution for Science Caption This is a screen shot from a video simulation of the canonical model of the Moon's formation, in which the proto-Earth was hit by a Mars-sized object between 4.4. and 4.5 billion years ago. Credit Courtesy of Miki Nakajima and Dave Stevenson. Usage Restrictions With 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.