164 ANNUAL, REPORT SMITHSONIAN INSTITUTION, 19 3 5 



fjeochemical papers the present discussion is borrowed) concludes 

 that the amount of " fossil " oxygen thus buried in the sedimentary 

 rocks is at least as great as that now present in the atmosphere and 

 may be twice as great. An amount of carbonaceous or other organ- 

 ically reduced material equivalent to both the free and the fossil 

 oxygen must also be in the sediments — which is not unreasonable. 

 Given time enough, this inexorable process of rock-decay might 

 exhaust the remaining oxygen of our atmosphere and put an end 

 to all that breathes. But this danger is indefinitely remote — a billion 

 3'ears away anyhow, since life has lasted that long and only half 

 the oxygen has been used up ; and probably much longer, for 

 volcanic gases are still carrying " juvenile " carbon dioxide into 

 the air that has never been there before. 



It is of no small interest, however, to look at Mars and see there 

 what looks very like the end of this process. The reddish color of 

 the i^lanet — unique among the heavenly bodies — is just what might 

 be expected, and indeed is almost inevitable in a surface stained with 

 ferric compounds. (The unoxidized rocks of the moon are gray or, 

 at most, brownish.) Wildt suggests that, in the thin atmosphere of 

 Mars, the ozonized layer produced by the action of ultraviolet light 

 at the top of the atmosphere should be near the surface — not high up, 

 as it is here — and that oxidation processes at the planet's surface 

 might thus be accelerated. 



It would be premature, however, to conclude that Mars must be 

 a lifeless planet. The depletion of oxygen would be very slow, and 

 plant life would probably adjust itself, as it has done on the earth 

 in response to far more rapid climatic changes. Whether animal life, 

 if ever present, could have survived is speculation. A race of no 

 more intelligence and engineering skill than our own could pre- 

 sumably meet the situation and survive in diminished numbers 

 breathing electrolytic oxygen, provided that it paid any attention 

 to changes so slow as to be imperceptible in a thousand generations. 



While Mars resembles the final stage of our suggested process, 

 Venus seems to be at the beginning, and much like what a lifeless 

 earth would be. We do not know how life began here, but conditions 

 may well have been much less favorable on Venus. Wildt concludes 

 that the powerful " blanketing " effect of the atmospheric COo, com- 

 bined with the stronger solar radiation, may raise the temperature 

 at the planet's actual surface to 100° C. or higher, in which case the 

 failure of life to develop is not surprising. The real puzzle is the 

 apparent absence of water on Venus' surface. She is almost a twin 

 of the earth in size, mass, density, and so on, and one might have 

 expected an ocean of comparable volume. Wildt suggests that all 



