22 HAROLD C. UREY 



ported glacial drift toward the equator. Since much of the surface was covered 

 with ice, carbon dioxide could not have reacted with the surface rocks and must 

 have remained in the atmosphere. Hence, high concentrations of carbon dioxide 

 would have reached the high atmosphere and the escape of atomic oxygen must 

 have been very rapid. When most of the water was lost, the carbon dioxide could 

 have reacted with the rocks and disappeared and the present situation with little 

 water and carbon dioxide would have developed. 



The evidence in regard to the development of the Martian atmosphere does 

 not preclude the existence of life on the planet provitling oxygen in large amounts 

 has escaped from the planet. It is Ukely that this is the case. The general chemical 

 development should have been similar to that occurring on the Earth during 

 its early history. 



CONCLUSION 



It is probable that the three planets, Venus, Earth and Mars, all originated 

 with substantial amounts of water on their surfaces. The estimated temperatures 

 are such as not to be prohibitive for the evolution and maintenance of hfe. 



This paper is a brief summary of certain parts of a much more detailed survey 

 of the problem of atmospheres which will appear in the Handbuch der Physik^ 

 where detailed arguments for many points mentioned will be given and where 

 more detailed references will appear. 



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