TOTAL YIELD OF PHOTOSYNTHESIS ON EARTH 5 



sea of the stable inorganic world, to the high plateau of organic life; it 

 finds its way back in hundreds of streams or meandering rivulets, which 

 set into rotation, as tlie.y hurry down towards the sea, thousands of little 

 wheels of life. 



B. The Total Yield of Photosynthesis on Earth * 



To acquire an adequate notion of the importance of photosynthesis 

 in the chemical household of the earth, it is interesting to estimate the 

 total turnover of matter and energy involved in this process. This can 

 be done, of course, only very approximately. 



The total yield of photosynthesis on earth was first evaluated by 

 Liebig in his famous book. Chemistry in its Application to Agriculture and 

 Physiology, whose first edition appeared in 1840. He estimated that, if 

 all the land were a single meadow with a yearly crop of 5 metric tons 

 (1 ton = 10'' g.) per hectare (10^ sq. meters), all carbonic acid in the air 

 would be used up in from 21 to 22 years. Considering the carbon dioxide 

 content of the air (c/. Table l.IV), this statement is equivalent to the 

 assertion that the plants utilize 10" tons of carbon dioxide and produce 

 3 X 10'" tons of organic carbon annually. Arrhenius (1908) and Cia- 

 mician (1913) made similar calculations, but assumed an average crop of 

 only 2.5 tons per hectare of land. (They gave Liebig's authority for this 

 figure; but according to Schroeder 1919, this was a misquotation). They 

 thus obtained a yearly yield of only 1.8 X 10'" tons of organic carbon. 



Ebermayer (1885) substituted a more elaborate picture for Liebig's 

 simplified assumption of "all land a single meadow." He distinguished 

 between wooded areas, cultivated fields, steppes and barren lands, and 

 added to the crop the roots and stubbles remaining in the fields. In this 

 way, he arrived at a figure of 2.4 X 10'" tons of organic carbon for the 

 annual production of organic matter by the plants. 



The next attempt, on the basis of improved statistical data, was made 

 by Schroeder (1919); the results are condensed in table l.I. Schroeder's 

 total of 1.63 X 10'" tons of carbon for the whole surface of the land, 

 corresponds to an average of 1.1 tons per hectare. Assuming that 15% 

 of the organic matter synthesized by the plants is used up by their own 

 respiration, this total can be revised upward to 1.9 X 10'" tons of carbon 

 per annum. 



In this estimate, the production of organic matter in the oceans was 

 altogether neglected. Schroeder made an estimate for the benthos, i. e., 

 the ground-attached algal vegetation of the continental ledge, and found 

 its contribution negligible compared to that of the land plants. As to 

 the free-swimming plankton, he saw no way of estimating its yield but 



* Bibliography, page 1 1 . 



