24 evolution: the ages and tomorrow 



tances, and they are the right size, which is equally impor- 

 tant. If a planet is too small, as is our moon for instance, it 

 will never be able to hold an atmosphere; if it is too large, as 

 is Jupiter, it will hold all the light gases present at its birth, 

 a condition eventually leading, together with other factors, 

 to an atmosphere in which hydrogen predominates along 

 with methane (marsh-gas) and ammonia. 



The elements most necessary for life will likely be present 

 at the origin of a planetary system since they are all in the 

 cosmos. The four important ones are carbon, hydrogen, ni- 

 trogen, and oxygen; but the greatest of these is carbon. Mat- 

 ter becomes alive through the inexhaustible "genius" of this 

 element with its unique and infinite combinations and, as has 

 been shown by H. F. Blum, through the unique "fitness" of 

 the others to combine with it. No other element possesses car- 

 bon's wide range of properties, although silicon is similar to 

 a limited degree. Chemistry is just beginning to visualize 

 fully the immense and endless Complexity of the compound 

 molecules which have carbon as a basis; and biology is justi- 

 fied in assuming that life wherever found in the universe 

 would be in essence of the carbon configuration. Water is 

 the medium of life and it must be present as a liquid, not as 

 ice or steam exclusively. The building blocks of protoplasm 

 are joined with, and in the presence of, water; and all the 

 complexity of the configuration of life is possible only in the 

 narrow temperature range of liquid water. This can be a 

 critically limiting factor for the appearance of life, since in 

 our solar system only the earth has the "cool, clear water" in 

 and out of which high life forms can emerge. The over-all 

 complex of environment is always the limiting factor. 



Venus is the right size and is not too near the sun, yet it is 

 wholly a desert world with no rivers, no lakes, no oceans. 

 All the land is a "dust bowl" beaten by unrelenting tornados 

 at insufferable temperatures. Great clouds of dust swirl high 

 into the carbon dioxide atmosphere. Obviously, no life 

 whatever is possible there. 



