CHAPTER XI. 



THE GEOLOGIC FUNCTIONS OF LIFE. 



I. THE DISTINCTIVE FEATURES OF ORGANIC PROCESSES. 



There is no reason to suppose that life processes, as we know them, 

 were in operation in the earhest stages of the earth's history. They 

 were introduced and developed gradually during its progress. With 

 life there came into the processes of the earth's development three dis- 

 tinctive factors: 



A. Certain chemical actions giving rise to compounds that are not 

 known to occur independently of life. 



B. Certain modes of aggregation of material, and certain kinds of 

 bodily movements, not known except in association with life. 



C. The mental element, under the direction of which certain new 

 processes were inaugurated, and certain previous processes were modi- 

 fied and controlled. 



A. The Chemical Work of Life. 



The peculiar chemical phenomena connected with life chiefly con- 

 cern the carbon compounds. In the inorganic world the carbon com- 

 pounds are few and simple. In the organic world they become extremely 

 numerous and complicated. These compounds are very unstable, for 

 the greater part, and their partial decomposition gives rise to many 

 additional compounds. Some of the true organic compounds and some 

 of their decomposition products have the power of combining with 

 inorganic substances, and so produce an additional series of semi-organic 

 combinations. The total number of the compounds thus directly and 

 indirectly connected with life greatly exceeds that of all inorganic com- 

 pounds. Their mass, however, is very greatly inferior. 



Life material chiefly atmospheric. — In the building up of the organic 



compounds, a necessary step is the decomposition of certain inorganic 



compounds. The chief of these is the carbon dioxide of the atmosphere 



and hydrosphere, the decomposition of which furnishes the carbon 



needed for the organic compounds. On this account carbon dioxide 



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