3 



Beginnings of Life 



To dress the stage so that life as we know it may appear, 

 is the work of a very special series of evolutionary processes. 

 Life's habitat must be exceedingly well placed and favored 

 as to the physical and chemical configuration: it must not 

 be too near nor too far from solar radiation; it must not be 

 too large nor too small; it must have large and easily ac- 

 cessible quantities of carbon, hydrogen, nitrogen, and oxy- 

 gen, besides a score or more other elements like calcium, 

 phosphorus, iron, iodine, and so forth. There must be water 

 for the colloids and emulsions of the living substance; in the 

 millions of degrees of temperature of the sidereal universe 

 there must never be in life's habitat a range long sustained 

 above the boiling point or below the freezing point of 

 water; and there must be evolved eventually, if high-level 

 mind is to appear, the forest and the upland meadow and 

 the ocean of the atmosphere. 



The distance of a planet from its sun will be the main 

 factor determining its surface temperature. In our solar 

 system. Mercury is much too close and is bathed in a fiery 

 furnace of radiation, the surface temperature of the sunny 

 side being high enough to melt lead. Jupiter is too far out; 

 it is a frozen world more than a hundred and fifty degrees 

 colder than ice. The same holds for all the outer planets of 

 our system, Saturn, Uranus, Neptune, and Pluto. None of 

 these could be the abode of any life we can imagine. Venus, 

 Earth, and Mars are situated at more or less favorable dis- 



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