BEGINNINGS OF LIFE 25 



Mars possesses some water vapor but no surface water. 

 On occasion, small white clouds of water vapor appear high 

 in the very thin atmosphere at the equator and are more or 

 less permanent over the poles. Yellow dust clouds appear 

 more frequently and are sometimes very large and persist 

 for weeks. Mars is an exceedingly dry planet with tempera- 

 tures ranging daily at the equator from well below freezing 

 at night to 50 degrees F. or so at noon. The very thin at- 

 mosphere may contain some oxygen, a sign that there has 

 been and still is limited plant growth. The seasonal greenish 

 markings on the planet are generally taken to confirm this. 

 However, D. B. McLaughlin contends that these markings 

 indicate volcanic activity and that the changes of color are 

 due to the reaction of atmospheric carbon dioxide and vol- 

 canic ash distributed by seasonally prevailing winds. In Mc- 

 Laughlin's view. Mars is a world where the stage for the 

 appearance of life is about to be set by the release of suffi- 

 cient water through volcanic action. This, of course, con- 

 trasts with the view of others that Mars is a dying world 

 gradually losing the last of its atmosphere. In any case, at 

 the present time the only possible life there is of a very low 

 kind, probably something like our lichens. 



The atmosphere of the earth is the result of a long evolu- 

 tion. It is doubtful if any atmosphere at all remained after the 

 hot, molten mass of our globe was individualized. Either the 

 gases of the air were boiled away by being too close to the 

 contracting mass of our nascent sun (the dust cloud hy- 

 pothesis), or they were lost due to the high molecular ac- 

 tivity of the gases. There is general agreement that we start 

 our history on a globe of molten magma without any appre- 

 ciable atmosphere. The cooling magma evolved water vapor, 

 carbon dioxide, and other gases but no great quantity of 

 free oxygen or nitrogen. Jeffreys suggests that the water 

 vapor was released when the silicates, which had been hold- 

 ing it, soHdified. One of the main sources of oxygen was the 

 production of glucose (sugar) in plants by the combination 



