Geological History of the Atmosphere, 99 



imposed by the conditions of the problem (so tar as these are 

 known): that is to say, they probably do not err by being 

 put too low. and indeed variations in the percentage of atmo- 

 spheric carbonic acid to the extent indicated may have taken 

 place in a much shorter time. For, as we have observed 

 already, it is quite possible that the amount of carbonic 

 acid annually restored to the atmosphere by the oxidation of 

 organic remains in various ways may not be more, and may 

 even be less, than 99*0 per cent, of the amount annually 

 removed bv the growth of vegetation and the weathering of 

 rocks; in which case we would infer that the normal or average 

 amount of carbonic acid of telluric origin annually added to 

 the atmosphere is not less than 1 per cent, of the amount 

 annually removed by vegetation &c. Now if we suppose, as 

 before, that the average annual amount of telluric carbonic 

 acid is increased by one-half of itself, and that the extra quantity 

 continues to be evolved steadily for a long time, then in 19,000 

 years the percentage of atmospheric carbonic acid would be 

 increased to 3 times its present value. On the other hand, if the 

 annual yield of telluric carbonic acid were diminished, and re- 

 mained diminished, by one-half of its normal quantity, then the 

 total amount of atmospheric carbonic acid would be reduced 

 by one-half in 4700 years. Further, since it is quite possible 

 that in periods of great volcanic activity the amount of car- 

 bonic acid evolved may be twice or even several times greater 

 than the average or normal amount evolved, and also since 

 it is possible that the amount evolved in very quiescent times 

 may be much less than half the average amount, it is evident 

 that very great changes in the amount of atmospheric car- 

 bonic acid may be brought about in considerably shorter 

 periods than 19.000 or 4700 years. 



We admit, of course, that in making calculations of this 

 kind, some allowance might have to be made for the effect of 

 an increase or diminution in the quantity of atmospheric 

 carbonic acid on the luxuriance of vegetation, and the activity 

 of other agencies which tend to remove carbonic acid from 

 the atmosphere. It is highly probable that in the event of a 

 large increase in the percentage of atmospheric carbonic 

 acid, there would be an increase in the luxuriance of vege- 

 tation on the earth taken as a whole (other conditions being 

 assumed to be as favourable as they are at present), on 

 account of the (hypothetical) increase in temperature itself, 

 and possibly also on account of the greater quantity of car- 

 bonic acid readily available for respiration by the leave- of 

 vegetables. The latter is a point of considerable interest 

 :md de>erve<5 investigation* ( K Wollny, who has done a 



II 2 



