SCENERY, SOIL AND THE ATMOSPHERE 579 



plant decay and from other sources. All these processes would take 

 from the air in geological time, many thousand times as much C0 2 as 

 it now holds. 



On the other hand, there have been gains through various sources 

 of supply. These are, from the ocean, and from the interior of the 

 earth by volcanic action, and in escape in connection with earthquake 

 movements. Any changes involving deformation and fracture open 

 the way for supplies of this gas from below. Van Hise lays emphasis 

 on C0 2 as derived from volcanoes 3 and in the same passage refers to 

 emanations from hot springs and mine waters. He quotes Lecoq to 

 the effect that the mineral springs of the Auvergne alone give off nearly 

 one tenth as much of this gas as is freed by the entire coal burning of 

 Europe. The same author includes meteorites as a source of C0 2 but 

 regards this means of gain as unimportant in later geological eras. 

 Possible supplies may have been received from the sun, if the projec- 

 tion of gases from that body is sometimes so energetic as to shoot them 

 within the orbit of our planet; and, as has been implied, there is a 

 steady restoration of this gas through decomposition of organic matter, 

 and through organic processes. 



As oxygen combines actively with some substances, notably iron, 

 we are to expect large losses of this gas from the atmosphere, when we 

 remember that oxidation has been a world-wide process, throughout 

 the history of land surfaces, down to the lowest level of atmospheric 

 penetration. Thus Smyth concludes a brief essay on this subject by 

 saying, " The abstraction of oxygen by iron is a factor that can not be 

 disregarded in any attempt to work out the geological history of the 

 atmosphere." 4 



There have also been compensating supplies of oxygen. The fixing 

 of carbon in the crust involves the freeing of oxygen. There have been 

 times of predominant plant life, leading to the abstraction of C0 2 , and 

 the release of 0, thus notably changing the atmosphere until animal 

 life enlarged its province, using and freeing C0 2 . Chamberlin thinks 

 that organisms have freed more oxygen than the rocks have absorbed 

 and that this gas therefore has had a growing part in the atmosphere. 



Nitrogen, as is well known, is the inert part of our atmosphere, 

 but is absorbed through certain bacteria, leading to modern effort to 

 utilize it in restoring the fertility of the soil. On the other hand, 

 some nitrogen is supplied to the atmosphere through volcanic erup- 

 tions. 



These views of atmospheric inconstancy involve general doctrines 

 of climate and earth history which are in the crucible of discussion. 

 The efficiency of the atmosphere as a thermal blanket is held to be so 

 dependent on the amount of carbon dioxide present, that moderate 



3 " Treatise on Metamorphisni," pp. 9G9-970. 



4 " The Abstraction of Oxygen from the Atmosphere by Iron," C. H. Smyth, 

 Jr., Jour. Geol., 13, 319-323. 



