26 evolution: the ages and tomorrow 



of water and carbon dioxide, encouraged by chlorophyll, 

 locking up the energy of sunlight (photosynthesis). Oxy- 

 gen was probably also produced in the stratosphere, accord- 

 ing to Malcolm Dole, by photochemical and ionization 

 activity from oxides of carbon and nitrogen. Nitrogen, too, 

 was introduced to the atmosphere by the activity of plants. 

 By the time of the formation of the solid crust, the atmos- 

 phere of the earth was chiefly carbon dioxide and steam; and 

 the latter was raining water onto the hot rocks to form the 

 oceans. 



Our earth is rich in water, but it could have been too rich. 

 A greater quantity would have forever submerged the land 

 and hence the highly active and intelligent land forms of life 

 would not have existed here. From the record it is permis- 

 sible to say that no high-level intellect can evolve as a 

 marine form; and again we find that psychic evolution in 

 any given situation is dependent on increasingly critical 

 circumstance. 



The stage is set and the drama of life begins, not with 

 any orchestral fanfare or flourish, but imperceptibly, grad- 

 ually, and naturally, molecule by molecule, following the 

 laws of structure and relationship that apply throughout 

 the whole universe. The special role in which the element 

 carbon has been cast is soon apparent, and the hydrocarbons 

 (compounds of carbon and hydrogen) appear. Even some 

 of the complex compounds of this group are found in 

 meteorites and in the dust of interstellar space. They were 

 formed on the earth even before the hot rocks had cooled, 

 through metallic carbides (carbon and metals) changing to 

 hydrocarbons in a reaction with hot steam. Hydrocarbons 

 are organic substances and are produced in association with 

 life; they are the primary compounds. J. B. S. Haldane 

 points out that ultraviolet radiation, now cut off by the 

 ozone of the stratosphere, penetrated to the surface and 

 greatly aided this synthesis. In the classical scheme of A. I. 

 Oparin nitrogen enters as nitrides of iron or calcium or 



