Earth collision (IMAGE) Harvard University Caption A Southwest Research Institute-led team updated planetary bombardment models with the latest geologic information and then applied those models to understand how impacts may have affected oxygen levels in the Earth’s atmosphere in the Archean eon, 2.5 to 4 billion years ago. This artistic conception illustrates large asteroids penetrating Earth’s oxygen-poor atmosphere. Credit SwRI/Dan Durda, Simone Marchi Usage Restrictions Credit must be given to the creator. License CC BY 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.