MAKING A HOME FOR LIFE 215 



For, without going very deeply into the subject, 

 it is clear that water was a precursor of life, just as 

 it .now is an essential concomitant of all vital 

 activity. Professor Henderson has worked out its 

 appreciation. " Water can dissolve a larger variety 

 of substances in greater concentration than any 

 other liquid"; "an enormous quantity of heat is 

 necessary in order completely to evaporate away a 

 lake or pond, and a smaller, but still very large, 

 quantity must: be given off before such a body of 

 water can freeze throughout its whole extent"; 

 the well-known anomalous expansion of fresh water 

 near the freezing-point conserves liquid water and 

 the life in it. And what shall we say of its capacity 

 for hydrolytic cleavage, or of the mobility of its 

 molecules, so important in bodily functions? 



But just as water necessarily appeared upon the 

 earth when the times were ripe, so carbon dioxide 

 was as necessarily present as a primary constituent 

 in the air, and the relations of the two made for 

 progress. For the law of the solubility of carbon 

 dioxide in water is such that at temperatures con- 

 sistent with the presence of a hydrosphere " it 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 

 extract it from the water." Moreover, the pres- 

 ence of carbonic acid in the rain enabled the waters 

 of the earth to mobilize in moderation the resources 

 locked up in minerals. 



The origin of living organisms upon the earth 



