417 



1. The organic life. Carbonic acid is fixed and converted 

 into organic substances by the assimilation of green plants. 

 It is liberated anew by the respiration of all living organisms 

 and especially by the decay of organic substances. This 

 circulation is generally performed in a very short time and 

 cannot have any considerable effect (as pointed out by Högbom) 

 on the quantity of carbonic acid present in the atmosphere. 

 Only that part of the organic substance, which is deposited as 

 such and in the course of the geological periods converted 

 into carbon and hydro-carbons, is permanently, or at all events 

 for a long time, withdrawn from the atmosphere. Through this 

 deposition the organic life of the globe constantly tends to 

 diminish the quantity of free carbonic acid. No small amount 

 of carbon has, undoubtedly, been fixed in this way and stored 

 up, partly in the layers of carbon and hydro-carbons, but, as 

 Chamberlin thinks, especially in the "disseminated organic matter 

 in the sedimentary series». If the immense length of the 

 geological periods is taken into consideration it would appear, 

 however, that the amount of carbon fixed year by year must be 

 comparatively small. 



2. The formation of carbonate from «alkaline» silicates 

 is a very important cause of diminution in the quantity of free 

 carbonic acid and has been recognized as such by several 

 Authors, who ascribe by far a greater influence to it than to 

 the action of the organic life. 



Högbom is of opinion that all carbonates on the earth are 

 derived from this source and, estimating their quantity as the 

 equivalent of a layer round the globe 100 m. thick (and pro- 

 bably more), he finds the quantity of carbonic acid contained 

 in such a layer to be 25000 times that of our present atmo- 

 sphere. He further estimates the total quantity of carbonates 

 yearly carried to the sea by the rivers in the world at 3 cb. km. 

 (corresponding to 4000 million tons of carbonic acid) of which 

 only a small part can be derived from the decomposition of 

 XXVI. 27 



