Early Earth (image) University of Colorado at Boulder Caption This is an artist's conception of the Earth during the late Archean, 2.8 billion years ago. Weak solar radiation requires the Earth have increased greenhouse gas amounts to remain warm. CU-Boulder doctoral student Eric Wolf Wolf and CU-Boulder Professor Brian Toon use a three-dimensional climate model to show that the late Archean may have maintained large areas of liquid surface water despite a relatively weak greenhouse. With carbon dioxide levels within constraints deduced from ancient soils, the late Archean may have had large polar ice caps but lower latitudes would have remained temperate and thus hospitable to life. The addition of methane allows the late Archean to warmed to present day mean surface temperatures. Credit Charlie Meeks Usage Restrictions None 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.