Researchers supported by the NASA Exobiology and Evolutionary Biology Program have adapted a three-dimensional, general circulation model of Earth’s climate to a time some 2.8 billion years ago when the Sun was significantly fainter than today. Their work indicates that the early Earth may have been more prone to catastrophic glaciation than previously believed.

The new 3-D model could help solve the “faint young Sun paradox.” Several billion years ago during the Archean Eon, the Sun’s output was only 70 to 80 percent of today’s levels. However, geologic evidence shows the climate was as warm or warmer than now.

“The ultimate point of this study is to determine what Earth was like around the time that life arose and during the first half of the planet’s history,” said Professor Brian Toon of the University of Colorado at Boulder. “It would have been shrouded by a reddish haze that would have been difficult to see through, and the ocean probably was a greenish color caused by dissolved iron in the oceans. It wasn’t a blue planet by any means.”

Understanding the environmental conditions during the Archaen is essential in determining how life originated and evolved on the early Earth.