12 The Nature of Biological Diversity 



do obtain, no life can exist on Venus at the present time. In the past, 

 liquid water may have existed on the planet, the pressure of carbon 

 dioxide may have been low, and hence the greenhouse effect may 

 have been less, the temperature lower, and living organisms may have 

 been present. It would be magnificent had life developed but dis- 

 appointing if it should have been destroyed. 



Mars is a very different planet. It has a thin atmosphere with a 

 pressure at the surface of about one-sixth that of the earth. Carbon 

 dioxide is present, but oxygen has not been detected. The atmosphere 

 is probably mostly nitrogen. It extends to a great height because of 

 the low gravitational field. It is most probable that both hydrogen 

 and oxygen can escape from the planet and hence that the planet may 

 have had extensive oceans in the past. Glaciers would appear to have 

 been probable in this case, but just because the rocks were covered 

 by them carbon dioxide may not have reacted with the rocks effec- 

 tively and the greenhouse effect may have raised surface temperatures 

 above the very bleak ones that obtain at the present time. Life may 

 have evolved on this planet and in spite of the very arid and cold 

 conditions it may persist to the present time. Carbon dioxide is present 

 as shown by its absorption bands. Water is probably present as indi- 

 cated by the polar frost caps and the morning haze, but the estimated 

 amounts in the atmosphere are very small. It is probably escaping 

 from the interior because both hydrogen and oxygen should escape 

 at such rates that the observable water would be lost in less than 10 e 

 years and hence atmospheric water must be continuously replaced. 



Life may be present on Mars and its origin would be similar to 

 that outlined for the earth. The changes of color with the seasons, the 

 persistence of the gray areas in spite of dust storms, and, as Sinton 

 (1957) has recently observed, the presence of faint absorption bands, 

 which can be ascribed to the CH band in the light reflected from the 

 gray areas, indicate that life may be present. The proof that this is 

 true would be the most magnificent scientific datum of the twentieth 

 century and would justify all the effort of the space programs of the 

 world. It would substantiate the beliefs of the many students of this 

 subject, namely, that life will evolve when conditions are appropriate 

 in many other places of the universe and that life on earth is not alone 

 in this vast expanse of space that extends for billions of light years in 

 all directions. 



References 



Abelson, P. H. (1957), Ann. N.Y. Acad. Sci., 69:276. 



Bates, D. R., and M. R. C. McDowell (1957), J. Atmospheric & Terrest. Phys., 11: 



200. 



