84 THE ORIGIN AND EVOLUTION OF LIFE 



is not their prime constituent, also adaptation to an earth-and- 

 water environment rather than to an atmospheric one. 



In our portrayal of the chemistry of the Hfeless earth it is 

 shown how the chief hfe elements essential for the energy and 

 nutrition of the nitrifying bacteria, namely, sodium, potassium, 

 calcium, and magnesium, with potassium nitrite and ammo- 

 nium salts as a source of nitrogen, may have accumulated in 

 the waters, pools, and soils. These bacteria were at once the 

 soil-forming and the soil-nourishing agents of the primal earth; 

 they throve in the presence of energy-liberating compounds of 

 extremely primitive character. It is important to note that 

 water and air are essential to vigorous ammonium reactions, 

 whether at or near the surface. In arid regions at the present 

 time the ammonifying bacteria do not exist on the dry surface 

 rocks, but act vigorously in the soils, not only at the surface, 

 but also in the lower layers at depths of from six to ten feet, 

 where moisture is constant and the porous soil well aerated,^ 

 thus giving rise to a nitrogen-nourished substratum, which 

 explains the deep rooting of desert-dwelling plants. 



A second point of great significance is that these nitrifying 

 organisms are heat-loving and light-avoiding; they are dependent 

 on the heat of the earth or of the sun, for, like all other bac- 

 teria, they carry on their activities best in the absence of sun- 

 shine, direct sunlight being generally fatal. The sterilizing 

 effect of sunlight is due partly to the coagulation of the bac- 

 terial colloids by the rays of ultra-violet light. The sensitive- 

 ness of bacteria to sunlight cannot, however, be viewed as 

 evidence against their geologic antiquity, because their undif- 

 ferentiated structure and their ability to live on inorganic 

 foodstuffs even without the aid of sunshine seem to favor the 

 idea that they represent a very primitive form of life.'- 



iLipman, Charles B., 191 2, pp. 7, 8, 16, 17, 20. -I. J. Kligler. 



