24 Importance of Water 



necessary to evaporate away a lake or pond, and a 

 very large quantity of heat must be lost before such 

 a body of water entirely freezes. 



Moreover, the relations between water and carbon 

 dioxide made for progress. At temperatures con- 

 sistent with the presence of a hydrosphere, the carbon 

 dioxide "must always be somewhat evenly distributed 

 between the air and the waters of the globe. Water 

 can never wash the carbonic acid out of the air, nor 

 the air extract it from the water." So much the better 

 for land plants and water plants that get all their 

 carbon supplies from carbonic acid. Furthermore, 

 the presence of carbonic acid in the rain enabled the 

 waters of the earth to mobilize in moderation the re- 

 sources locked up in minerals. We need not prolong 

 the panegyric of water save in recalling that living 

 matter itself contains at least 75 per cent of water. 



Another significant fact is that the surface of the 

 young earth must have shown an abundant presence 

 of carbon, hydrogen, and oxygen in combination. 

 These three elements form, we may almost say, a 

 great triumvirate. "Of all the chemical elements," 

 Professor Henderson reminds us, "hydrogen, carbon, 

 and oxygen possess the greatest number of com- 

 pounds and enter into the greatest number of re- 

 actions." The}' tend, if we may say so, to join hands, 

 to form rings and groups. The atoms of carbon 

 possess the power of uniting in long chains which form 

 large molecules, and it is this power which has made 

 the compounds of carbon so numerous, so complex, 

 and so important. 



