What was Earth like 2.8 billion years ago?  The first life was emerging on the planet.  The Sun was weaker than it is today, but geologic evidence shows that the climate was as warm (or warmer) than it is today.  Was Earth colder because of the weak Sun, or warmer, as geologic evidence suggests?  How did this affect how life arose?

A new 3-D model of early Earth suggests that the planet underwent significant changes–from very warm to very cold.  Past models were one-dimensional–holding constant the amount of cloud cover or sea ice–to make the calculations easier.  But with more advanced computing, researchers at the University of Colorado Boulder were able to make better models of the planet’s climate.

“The inclusion of dynamic sea ice makes it harder to keep the early Earth warm in our 3-D model,” Eric Wolf, doctoral student at CU-Boulder’s atmospheric and oceanic sciences department, said. “Stable, global mean temperatures below 55 degrees Fahrenheit are not possible, as the system will slowly succumb to expanding sea ice and cooling temperatures. As sea ice expands, the planet surface becomes highly reflective and less solar energy is absorbed, temperatures cool, and sea ice continues to expand.”

The scientists’ model shows that Earth was periodically covered by glaciers, but the geologic evidence suggests that it was much warmer than that.  The calculations show that an atmosphere that contained 6% carbon dioxide would have kept the temperature high enough for life to thrive, but the soil samples show that the carbon dioxide concentration was not that high. So what’s the warming mechanism?  Eric Wolf and Brain Toon are still searching for it.

Since the 3-D model takes so much computing time (up to three months for a single calculation), we’ll be waiting a while for the answer.

“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 Toon. “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.” By the end of the Archean Eon some 2.5 billion year ago, oxygen levels rose quickly, creating an explosion of new life on the planet, he said.

And along the way, better models of Earth’s climate will come out of this study, enhancing scientists’ ability to predict what Earth’s future might look like, and scientists will learn more about the conditions of early Earth, which could help in assessing the habitability potential of other planets.

Explore the interactions of greenhouse gases and ice sheets in the High-Adventure Science climate investigation, and explore the search for extraterrestrial life in the High-Adventure Science space investigation.

http://www.sciencedaily.com/releases/2011/12/111205140521.htm