FAYETTEVILLE, Ark., July 19 (UPI) -- French and U.S. scientists said a thermodynamic study of Martian clay soils suggests inconsistencies in theories of a thick carbon dioxide atmosphere.
The study -- led by Vincent Chevrier of the University of Arkansas and Francois Poulet and Jean-Pierre Bibring of the University Paris-Sud -- found little carbon dioxide could have been present during the soil formation. That finding contradicts a popular theory of the early Martian atmosphere.
Researchers said Mars' gullies, valleys and clay formations suggest a wet past since nearly all clays formed on Earth do so in the presence of water or extremely humid conditions.
Therefore, the clay remnants of ancient Mars led scientists to hypothesize the earliest era on that planet, the Noachian period, had a carbon-dioxide-rich atmosphere that created a warm, wet surface with liquid water.
But in a carbon-dioxide-rich environment, clay formation would be accompanied by carbonate formation -- and Chevrier said current studies of Mars have found no such compounds.
"If you had a thick atmosphere of carbon dioxide, you should have abundant carbonates," he said. "So far no one has seen even a grain of carbonate."
The research is detailed in the journal Nature.
